They're not bad, those Fender Vibro Champs, you might be able to upgrade the speaker to a 10 inch one, although you might have to replace the stock front baffle to be able to do so, I've got a Guitar Classics magazine that has an article about upgrading the speaker in a Fender blackface Champ with a 10 inch speaker, so it is do-able, apparently the author of the article reckons the speaker upgrade made the amp sound a lot better.
The Super Twin is sounding pretty good with my pedal board setup, I'm really surprised at how well the amp takes pedals, it's got tonnes of headroom due to the six 6L6 power tubes being connected up in what's called the "Ultra Linear" configuration, this means that the six 6L6 tubes can put out quite a fair bit of power, 180 Watts R.M.S. (R.M.S. is short for Root Mean Squared), and a peak power output of 395 watts, all at low distortion, I don't really need to crank the preamp and master volumes up much, about three for both is loud enough for my loungeroom, having tonnes of headroom means that the sounds I get with the pedals are going to be pretty clear, the bright switch definitely has an audible effect, the amp sounds warm when the bright switch is turned off, but there is still plenty of highs in the tone so it doesn't sound muffled, I've been spending a bit of time familiarizing myself with the amp, getting to know it and how to get good tones out of it, the funny thing is, some Super Twin amp owners say that it's hard to get a good tone, but my experience has been the exact opposite, I've found it really easy to get good tones, I've done some experimenting with the 5-band EQ and you don't have to do much with it to get some good tones with that either.
The amp definitely sounds better with the footswitch plugged in though, I like what the volume-boost footswitch does, but I'm not a big fan of the amp's built-in distortion, fortunately I can easily use a distortion pedal instead, the red JD-F2 Fuzz Face sounds great through the amp, as does my TS-9 Tube Screamer and BD-2 Blues Driver, the other pedals broaden the tonal palette I've got to work with, and I can use them to doctor clean tones if I want.