I'd recommend sticking with Item Rack. Although it does not use Ace, this does not mean it is a bad mod. Gello is an excellent coder and his mods are top notch. Although Ace is awesome, it is not the end all and be all of addons.
Definitly wasnt desparaging the performance of features of the addon, that being said I've become accustomed to some of the approaches taken in Ace addons. Configuration menus that can be disabled, simple menusets (dewdrop?), and in general it feels like Ace addons end up being more feature rich then others and I suspect it has something to do with the mundane stuff (infrastrucutre, event handling, etc) being already done for the developer which in turn allows them to focus on features. My guild goofs on me for being 'a robot' with all the addons I run but the older I get the slower I get and some of these features just make me a better player. I dont know how many times I've died forgetting to wear my Ony cloak, heh. Let alone remember to swap one of my 10,000 hard earned trinkets when the little -Combat goes by my screen.
I've been hooked on the ACE2 addons now for a while and find most of them better in ever way then non ace'd versions. How does the community keep track of what's in the pipeline (does it do that?) There are still some pretty big gaps in my addon set that I'd love to throw away and well I'd track/test any in in progress of the following:
Lets face it raiding is the name of the game for many of us in WOW. Several areas in the raiding game are still rather tedious and or could benefit from 'smart people' created addons. I spend lots of time every boss encounter rearranging groups to match the raid encounters needs, this boss need 7 tanks, need to know their specs, their armor, priest mana yadda yadd. I spend even more time keeping track of who I've added or placed 'on deck' for DKP purposes. I have to keep the 'fatty' CT_RaidTracker so that I can import DKP strings without loosing my mind and then I spend another 1 hour (per raid) trying to rework that string to fit our DKP policies. The lack of DKP management tools in the game and the klugy nature of most of them really begs for an ACE'd addon. My entire guild has changed to BigWigs for boss event handling and if that level of talent was put to this problem I can tell you for sure many would rejoice!
Item / Trinket Management
I use a hodgepodge of stuff today AceWardrobe for gear sets, trinket menu for trinket swapping, auto-bar styled clicky management but the amount of tools out there to manage 'clickables' is really insane and most of these tools are pretty '1st generation' in look feel and functionality. One of the better gear managers Item Rack is awesome functionality but having made the ace swing months ago I'm now facist about my memory consumption.