I personally use Launchbox myself and love it. I'm confused why you feel LaunchBox is only useful with emu-paradise. It's a great front end for any emulator which are accessible from many different sites.
Emulators are usually free, but not always. Emulators are also 100% legal on their own. Some may require you to acquire a BIOS that should come from a legal source.
When it comes to ROMS this is the real grey area, but it's only really grey because it's so different depending on where you live. I live in Canada, and we have a law that protects us when we wants to use software we've purchased a license for in a way the developer/distributor didn't intend. We can copy the original disc/cartridge as long as we don't distribute and the original/copy aren't used at the same time. We're protected from prosecution when downloading a copy of software we already own from a third party source, but since the other person would have to be illegally distributing it to accomplish this, it's technically illegal still.
To my knowledge most states, and other areas in the world, require you to get the game from the original source but even that is illegal in some places. You'll have to look how laws specifically affect you in your area. I personally believe you should have a right to reuse software you've purchased. You could choose to download the ROMS at your own risk. I've never heard of someone being prosecuted for it.
Oh, an in regards to games the developer might have abandoned allow you to download for free. Version of the games that are published on consoles can still be protected by the publisher. For example a developer might have a copy of a game on PC, SNES, and Genesis that they say is now abandonware. But if Nintendo doesn't agree that may still make it illegal to download the SNES copy.