I have a Bally Lost World I recently received as my first pin, and it had a horrible dimming problem when I first brought it home. When I got the pin, it was the first time the machine has been significantly moved in ~15 years, so I think between the jostle of transporting it in a truck along with all the disconnect/reconnect of the plugs really did a number on all of the PCBs.
I haven't had a chance to reflow the solder on all the other connections, but I did reflow the connectors on the power board and that made a huge difference in the dimming. It still dims, but nowhere near as much as it did before. I also changed out all of the #44 bulbs to #47, which seemed to help some, too. I think I may order several of the fix-up kits from
http://www.bigdaddy-enterprises.com - the prices look very reasonable to me for all the work that goes into putting together the various "kits." Lindsey's advice is pretty much exactly what I have planned overall for my Lost World.
Also, I have found this site very useful in learning about my Lost World:
http://pinwiki.com/wiki/index.php?title=Bally/Stern
I have a bunch of other quirky issues with the game - sounds will sometimes get funny after playing a while, it looks like the battery is dead since no scores are being retained, etc. So I think I have a bunch of basic "Bally Maintenance" to do with all the connectors, capacitors, and battery. I just haven't had the time to dig into things - the kids are having too much fun playing.

I'm trying to consider the amount of money I should put into the game right now - although the machine was HUO since 1983, it hasn't been well maintained so the cabinet and playfield is pretty thrashed. Luckily, I got the game for free.