Recently I've been messing around with mic IRs to help colour some synthesized sounds that I use. (Modo Drum to be specific.) But as an experiment, I decided to try a mic IR on Eleanor Forte Lite and got some good results.
Below is a short song sung twice, the first time without a mic IR (100% dry) and the second time with a mic IR (100% wet). They have been level matched so you won't be fooled by a change in volume.
No EQ (apart from the IR itself), no compression, and no effects. The difference is subtle, but the mic IR does clear up some mud. Pay particular attention to the held vowel in "song."
There's a bunch of free mic IRs available here:
Microphone Impulse Response Project
The above collection is all "vintage" mics, complete with a smattering of broken mics, which could be interesting for special effects.
Unfortunately, the mic IR that I used in the above demonstration is not free. I bought it from PastToTheFuture. It's an AKG C12 IR using a cardioid pattern placed at 2 inches. You can get it as a single mic package, or in a collection package with a bunch of IRs.
Note that IRs only capture a static frequency response of a microphone, rather than a real-world dynamic response. Additionally, all voicebanks have either been recorded with a microphone (concatonative) or trained with a microphone (AI), so they've already been coloured by a microphone. By using a mic IR, you're essentially recolouring a precoloured signal.