I have a Classic 30 too. Bang for buck they're incredible. I've been looking for a new amp for a while and I haven't found anything much better for twice the price, so I'm leaning in two directions at the moment:
1. Spend THREE times as much (SRRI, Orange Rockerverb 50 combo or H&K Duotone combo).
2. Squeeze what I can out of the C30.
My investigations (by no means exhaustive!) on the second direction have led me to the following:
There's a range of possiblities, and opinions differ widely, but the following is what I plan to try if I don't upgrade the whole amp:
Preamp V1 - Tung-Sol 12AX7 re-issue (the tube in this spot affects the amp's tone the most)
Preamp V2 - JJ ECC83S
Preamp V3 - JJ ECC83S
Power Tubes - JJ EL84s (matched set)
There seems to be a lot of owners on the Peavey forum who like Greenbacks in there, as well as some who favour Weber Blue Dogs. I got a recommendation for 50W Weber Alnico Silver Bells from Eurotubes ... I asked for something that would give me better touch sensitivity and dynamic response and a smoother overdrive.
As the previous post says, there are more than a few owners who swear by the 1x12 extension, and I seem to remember a Greenback in the combo and the stock Blue Marvel from the combo in the extension cab is a good way to go. Peavey don't make the 1x12 extension cabs (112e) anymore and I think they're quite hard to get 2nd hand though ... might have to go with a non-matching cab.
Have a search on the Peavey forum and on here for more information and other viewpoints.
Good luck ... and enjoy your amp ... as others have said, and I agree, pretty tasty straight out of the box.
I bought a new Tweed Classic 30 when they first came out.
The best speaker I've found for it is the Mojotone BV-30H.
I did have a Vintage 30 in it for some time, which sounded BIG,
but it had that mid-hump I didn't like. The Mojotone is just clearer
and has sweeter mids and highs, as well as good bottom end.
I also tube it with all JJ tubes - ECC83S's and EL84's. Good tubes
for this amp.
I also recently installed the Peavey Tube Guard for it - I got from the Peavey Parts Dept.,
and they paid for shipping. It's a good addition, as I've broken a tube in this amp before.
There are also after market tube guards for it - just do a Google search and you'll see them.
I sometimes use JJ power tubes in mine, but I've never liked the JJ pre-amp tubes in the C30. I've gotten much better results with NOS Mullard's or RCA's. JJ's make mine sound like someone threw a blanket on it.