I've tried to do this, even to the point of using the same tubes in a modded and un-modded module...it really doesn't work...something in the signal chain or recording workflow loses the feel and subtle changes in sound..heck, my playing isn't consistent from one moment to the next.
If you want to try and get a feel for it yourself, get the same values of different types (orange drop, silver-mica, poly, ceramic etc. )of capacitor and change c3..it's the easiest way I can think of to hear a difference...it's subtle, but it's there...if you like what you hear/feel, then a mod might be for you.
My ear isn't that great tho'..yours may not be either...
NOTE: Pete uses his expertise and ear to change others in the tone stack too..but c3 is the simplest one to experiment with.
Just for reference, I've had:
Pete SL+/800 Bass switch
Recto Orange/Red Proto + bass switch
Recto Orange/Red 'Production'
1st gen mid-shift XTC
New mod mid-shift/gained XTC
Pete Twin/Deluxe switchable
Pete Ultra Lead bass/(voicing?) switch
...I may have missed one, but not a single modded module has sounded worse than before..all have had better sound and/or features.
The only one that didn't really work for me was probably the Ultra Lead but honestly, that module is kinda one-dimensional anyway (could be my fault in the way I use it and my shitty lead playing.