There's only a certain amount you can fall behind on the caster curve and still be capable. If you are 10 levels behind, you can't penetrate the SR of creatures your level and your spellcasting doesn't mean anything.]
Well then, Frank, perhaps you need to acknowledge that AT's can cast spells that do not need saves or SR checks. Every high level AT I've seen that has been top-tier (I've seen, played with, and DM'ed a number of them) goes this route. They don't need Spell Focus or Spell Penetration feats. EVER. Evard's Black Tentacles, Sonic Orbs, Acid Fog, you get the picture. Bolstered by spells like Telekinesis, Web, SM spells, etc., and you've got *firepower* that is just as efficient as the Mage who casts 3 levels higher than you if they had cast the same spell.
Given: Arcane Tricksters are powerful at high levels. Query: How do I become good and survivable at low and medium levels?
And the given assumption is false.
According to *you*! Your gaming sphere of influence must have short reach. AT's have been proven time and time again to be capable and strong at high levels. Your assertion is nonsense, based on the fact that AT's are popular for both their flavour and upper level power synergy. People the world over do not play high level AT's because they suck. I will admit, I've seen people mismanage the class ability ideosynchracies of the AT over the years. And that's why I go back to my earlier post that the high level AT really pops when played in the hands of an expert player.
"Is it sufficient to fulfill your character concept to be a Rogue who uses Wands with UMD?"
You keep hinging your argument that the Rogue is superior because of magic item accompaniment! And you do so without comparing an AT with gold-equivalent magical items in *his* possession! Add to the fact that UMD is not always successful for a Rogue, while it is for an AT (assuming Wiz/Sorc spell items), and you have a skewed comparison. AT's *with* magic items are even more superior than the Rogue with magic items. As now the AT can use his vast selection of spell and resource spell slots on one mandatory magical buffinsgs or attacks.
==============
Regarding your prior post:
Personal Spells are nice. Heck, if there was a personal spell that could give you back your five levels worth of sneak attack, and your four points of base attack bonus, and your seventy skill ranks then it would be totally worth it in spades.
Oh please. 9th level spells are "nice"?

You don't need a maxed Bluff when you can cast Suggestion, Charm Person, or Dominate Monster ... or hell, just DimDoor your way past the guard. You don't need a maxed Disguise skill when you can cast Disguise Self, Alter Self or Polymorph. You don't need a maxed D. Device skill when you cast Knock or Shatter. The list goes on and on. Spells *are* your Rogue skill equivalents in an AT build. And in many many cases, they exceed those skills capabilities. And don't forget ... the AT has a pretty nifty set of skill ranks himself, especially with his high INT nature.
And note: these spell are inherent abilities, and not provided by a freakin' Cohort, team-friendly mage, or reliance on a possibly-failed UMD check.
Rays + Sneak Attack is lame.
Try telling that to thousands of monsters that have died efficiently and quickly to this combo. And again, good AT's don't use Fireball, Lightning Bolt, or any of those other nonsense DC & SR based spells.
Less damage, and less uses per day. There's no good reason to use sneak attack on a spell when sneak attacks on bottles of crap do more damage right out of the box.
AT high level? Wrong.
The AT is casting 2 high level Rays per round (one quickened). If you are using spells like Prismatic Eye (MoF book), you are getting even more attacks per round at higher damage than if using your "Vials of Crap". You can add in other high-level hijinx combos that involve spells as Simbul's Spell Sequencer, Stars of Arvandor, etc. to get more attacks and/or damage potential (through potentially, more sneak attacks) per round than a comparable Rogue.
Hell, I've cast Hail of Stone and gotten SA damage on 5 out of 6 targets (because I had to make attack rolls on each potential target). That's something a Rogue could not have done. And *that* ... was my Quickened spell.
So what? It's a team game. You have a party wizard. If you don't have a party Wizard, there's a feat called Leadership that gives your party a wizard. And then the problem is completely solved. The ability to "not have to rely on a party wizard" is as meaningless as the ability to live without drinking water. Sure it's sometimes flavorful, but since the game actually includes you having the thing that you don't need - it doesn't actually make any difference whether you require it or not.
I'm with you on the "Team Game". I don't believe in mavericks or solo charging types. And I see AT's working well within a teamwork synergy concept. The no save/no SR spells I told you about earlier are classic battlefield management spells that also stalls enemies to allow prep and positioning actions by you and your allies. A good AT *still* has slots to allocate to buff his allies (Enlarge Person is a classic - it's arguably the best 1st level spell in the game) in addition to providing them divinations. After all, he is probably the party scout as well, so all those Detect Thoughts, Clairvoyance, and Scry spells are definitely mandatory for an AT. And spells as such as nowhere near considered to be selfish. Divinations help entire partys prepare, stay informed, stay on track, and avoid dieing.
In summation, a savvy AT player will have to spend some serious time allocating his spell slots and spell selections. He's not a blaster mage, even though he has characteristics of one (Rays + SA). He also has to accomodate spells to work with his scout, Rogue, & party buffing duties. Is this like stuffing 10 pounds of goods in a 5 pound bag? It can be, that's why the AT is not for one-dimensional players. At high levels, a 1 level dip into Mage of the Arcane Order can pay off huge utilitarian dividends to an AT. That's 8 or 9 spell level slots (combined total) to put into 1st through 3rd level utility slots to ensure he can effectively address all his roles. And when doing the sometimes awkward "Calling" of his spells via Spell Pool, he can do so while hidden or invisible ... where he won't get caught like a standard Mage would be doing his calling out in the proverbial open.
So yeah, Frank ... those 9th level spells are indeed, "nice" for an AT Rogue. Nice enough to make him a high-level star when adventuring amongst his fellow highly min/maxed compatriots. You just need to acknowledge that he has his shtick. If he is in a big party, he becomes even more powerful, as he can focus his spell arsenal on a neccessary party niche role. If he is in a 2 or 3 person party, not many people would pass on having the AT be able to perform admirably in 2 key roles.
Regards,
Lee