Just wanted to add some comments on the dim bulb tester (which is basically a plug with a lightbulb in series - check out this link:
http://www.antiqueradio.org/dimbulb.htm).
The dim bulb tester is a good way to go and any newly acquired old radio or newly worked on old radio should only be switched on while using one. For a normally operating 5 tube radio a 60 watt bulb should glow dim while the radio is on. If it glows brightly right away there is a short circuit in your radio somewhere. The link describes some other tests you can perform with the dim bulb tester.
The general consensus these days seems to be that recapping will not hurt the collector value, but some people go to such lengths as matching wire colors, refilling aluminum cap holders, and even hollowing out the original paper/wax caps and putting the new ones inside the old hollowed out one. I haven't yet, but on a very special or valuable radio I would perhaps consider taking the trouble. It may not be a problem with collectors in 2009 but who knows if it will matter 100 years from now.