I've played BT runner and was very impressed. I have not played the other games but have seen the BT compilation for the Wii. Is it worth the purchase for all the games?

Yes.
If you can find it, it should be worth about $20-$30
Not only does it come with the other Bit Trip games, but also bonus levels for Runner, as well as every other Bit Trip title, that you won't find on the Wiiware, nor 3DS versions.
The other games may not be as beautiful, or entertaining (in my opinion, anyways) but they are still easily worth your money.

I've also played Runner and enjoyed it quite a bit. But the disc is not more than an interesting collection of unusual mini-games. I would rather spend my money for "real" Wii games.

I'd say no, Runner 1 is the only game in the collection I liked. Everything was just bleh to me. Out of the roughly 50 Wii games I've bought it's the only one I really regret purchasing. It'd say save your money for Runner 2. Everyone of those games has a WiiWare demo, and those demos show you everything you'll do in those games so if you like those demos go for it, if you don't skip it.