Stationary spin bike vs trainer

They'll give you a workout but they will not help you with your bike time/speed/comfort because it's a completely different setup.

Get one of these:
http://www.probikekit.com/display.php?code=Y2007

You can only use that tire on the trainer but that's what the tire's made for. If you only wrote back after you wore out that tire, we'd hear back from you in about 10 years or so.

My impression is that spin bikes provide a pretty good bike workout if you set it up as close to your normal position as possible.  After a hard ride on a spin bike my legs feel very similar to how they feel after riding my tri bike on my trainer.

That said, I still try to do most of my indoor riding on my tri bike + trainer since I figure that's a little closer to road riding than a spinner.  I've got a Kinetic fluid trainer and haven't had any problems with excessive tire wear, even without using a trainer tire.  I'm currently using an extra continental ultra sport tire that I had laying around.  I used the same tire last winter and no problems so far.  Once it wears out, I'll buy a trainer tire.

Good luck!