I've played both 18/2 wiz/rogue and 20 wizard, and think both are great options. My general thoughts are that from levels 1-19 the wiz/rogue was more enjoyable to play, and at level 20 the pure is a bit more enjoyable.
I went drow (blasphemy!) on the wiz/rogue, and enjoyed the couple of extra skill points the starting 20 int afforded, allowing me max search/disable/umd/concentration, with a good spot and good-enough open locks (every lock except the non-essential Fleshmakers one). I had no-fail heal scrolls and raise dead, and regularly scrolled out divine buffs when needed. I would occasionally miss on spell pen checks, but nothing at all that made me feel gimped, even at end-game.
The wiz-rogue is often mentioned as a great solo build, and it is, but it is also hard to think of a more party-friendly build -- especially if you often run with strangers. You have better trap skills than pure rogues other than mechanics, you have the full slate of arcane spells, and you can spot heal/raise in raids that have more limited roles for arcanes.
The benefits of the 20 wizard are also obvious, so this doesn't take away from them; I'd recommend you try both out at some point.
My current wizard is soon to start her third life as a sorc, then will be back to 18/2, this time warforged or human. Having two wizard past life feats will at that point make the spell pen loss from the 2 levels of rogue even easier to swallow.
If you solo and shortman content a lot, then the 2 rogue w/ the ability to disable traps, pick locks and extra survivability will be very nice. However, for end game content (especially raids and epic), you'll probably want to be pure with maximum DCs, spell pen, etc. During leveling, the extra survivability and flexibility of 2 rogue will be really nice, but at end game it just isn't worth it or necessary.
Sounds like you should stay pure. My guess is improved spell pen etc would be worth more to your party than evasion for most end game content.
Sure, splash 1 level of rogue if you want rogue skills, or 2 if you want evasion (evasion being less important than skills and getting less synergy with an arcane build IMO).
I've had fun with a wiz/rogue, but for elite end game content, my pure caster was basically always the best choice.
I haven't played a pure caster to 20.
My character is a WF 11wiz/2 rog. He has Evasion and Insightfull Reflexes -otherwise it's not worth it. Evasion save me many times. I 'm using a +4reflex ring , cast greater Heroism and I can stand in the traps taking no dmg in normal difficulty. It is very nice .
But if you are always in a group with rogue then you'll be fine going pure I guess.
That is well known and nifty. It also, unfortunately, means you have to like WF. I don't (although I will admit, I recently made a WF FTR that I am having a blast with). Never really have. But that is purely for story, look and concept reasons. Fortunately for me, I am doing quite fine with my drow wiz, although I do go through healing pots like an alchoholic with a cask of Night Train. It also can not be said enough that, many people play this game and make chars that they envision being or playing. It takes a little more skill and caution to play non WF arcanes, to be sure, but they can be just as effective, (if not more, in drow case if only wanting pure dps / DCs).
Just wanted to pipe in with that info, as I see a lot of people asking about playing non WF wizards / sorcs nervously, as if there is something actually wrong with it, or they wont be effective.
You can do all of that except disabling traps on pure wizard, no reason to splash rogue for it. And as for traps, as others have said, convenient when leveling as there may be an occasional elite trap you can't simply walk through, but really not useful at 20.
If you're doing it to "contribute" to a group, then go full wizard, other classes can splash rogue and actually get full benefit out of what it offers like the haste clicky and sneak attack and they can do the disable traps. Or of course you can just invite a rogue. You know... the guys that kick wizards in the head for the amount of DPS they can put out.
For survivability go warforged sorc. Half-recast time reconstruct > wizard long recast spells.