you could say evasion is not needed, you could argue 2 caster level+capstone is more useful than evasion, but saying evasion is not useful is plainly wrong. when you can barely survive with 300hp, it doesn't mean an additional 100hp is not "useful".
when you have more HP, you can survive when taking more damage. when you have high enough reflex save (and evasion), you'll take less damage that work essentially the same as getting more HP. both of them mean better survivability and give you more options in game playing. e.g. you could more aggressive rather than staying behind to avoid damage, you could use your mana to kill rather than to cast protection, you have better chance to survive when you hit by traps/spells etc.
how about trying epic DQ2. it is imho one of the few quests that has extreme reflex save/evasion requirement.
before I TR'd my second caster, I have a wiz20 and a sorc18/monk2. both of them are fleshy, have 30+ reflex save and can use heal scrolls with no failure, the wiz has 100 more hp, better dps and spell DC, better healing amp, but I always prefer to use the evasion sorc in DQ2. In DQ2, it's not hard to get hit by bb for a few times in a row (and at the same time get hit by archers and efreetis), each blade hit at around 80-100 damage. During I-am-war, when i need to keep my wiz alive reliably, I have to top her HP regularly because I know her HP could drop by 200-300 easily in any time (and my scroll healing may be interrupted), say, 1 failed save 100 + 3 saved bb 50x3 + some archer/efreeti damages. When I run my evasion caster, I'll heal only when I get lower than 1/3 hp or 100hp as I take damage and fail to use scroll only when i have very low roll.
for competent players, say, when using a low reflex save fleshy sorc, he probably can survive by putting more focus in dodging and self-healing, but in this case he'll contribute less dps.
and for many epic quests, spells like DBF, chain lightning, bb are not always deadly but often cause a lot damages. I am not saying every wiz should go for evasion as it involves some tradeoff, but any wiz should take insightful reflex to reduce those damages as the feat is not that costly.