"What is the difference and comparative advantages between spinner bait, crankbait and jigs? (Jigs are actually a mystery to me: I can't pin down exactly "what" they are)"
I do a lot of bass fishing and will give it a shot - you might also check out my subjects list of Bass Fishing sites - lots of info there. Click on the "Subject" Bass in the column on the left of my pages.
A spinnerbait is a good reaction bait - you can cover lots of water with it fast, and you land almost all fish that hit it. Fish also tend to be bigger than on other baits, in my experience and opinion. It also works good in cover like trees and around stumps. You can fish them from bottom to top at a lot of different speeds. There is an excellent post on the forum about how to fish spinnerbaits from Lipjerker in North Carolina.
A crankbait is also good for covering a lot of water fast and catching lots of fish. I think smaller fish are more likely to hit crankbaits than spinnerbaits or a jig and pig. They hang up easier and work best on rocks or smooth bottoms - hard to get one through a treetop! Also, fish tend to come off them pretty easily. I have started a thread on the forum about crankbaits.
A jig and pig is definitely the best bait for big fish, but you will get fewer bites. It is a bait you almost have to fish slowly,so you can't cover a lot of water. Pitching one around heavy cover is how a lot of tournaments are won. You can fish in the cover without hanging up, and land most fish that hit it. Denny Brauer has made a fortune fishing with a jig. Go to the forum for tips and tactics on jig and pig fishing.
A jig is usually a leadhead with either a plastic or hair tail. It looks just like a baitfish and is a good finesse bait - when the bass are not feeding. Swim it along and it looks just like an easy meal. It is best in clear water on fairly light line. I use Sliders when the fishing is tough. Do you use jigs?
Hope this helps. Please post your question to my forum - you should get some good help there.