check the thread halfbakedstrat posted, it's got some good info on them.

Mod wise, for me personally, I wouldn't mod it at all, depending on the speaker that's in it, I may consider changing it, and as I enjoy reverb I'd consider the upgraded reverb as it seems to make a good difference.

You can go mental and look at different valves, caps, anything but you'll never change the core of the amp, it is what it is, a £500 amp that is fender voiced.

That said I've played blues Jnr and got good sound out of them, I've got a Blues Deluxe that after I did a valve swap out on to ones I like and resolved the well known all or nothing volume problem it came to life and sounds great, I sometimes take it out over my higher value amps.

The amp is what you make of it, yes you will be limited but that doesn't mean it's bad.