Clipless Pedals

the problem you'll have is the investment in clipless pedals and shoes will be more than the bike is worth! between pedals and shoes you are in for at least $100 (that's with cheapy pedals and shoes) but to your second question, you can move them to your next bike no problem. Once you've tried clipless pedals, there's no going back!

and the cheapy pedals aren't that bad either. I ran a set of Wellgo's for over 10 years! I only recently upgraded when I added another bike to the stable! I now run Shimano SPD 520's (MTB cleats) and Lake 200 mtb shoes (I like to be able to walk and run in bike shoes, mtb shoes have a recessed cleat so that you can still walk and run!)

Worth the investment - Yes!
Move between bikes - unless you have some very off the wall cranks or very old cranks they should move to your next bike.

As for cost, watch the classifieds here, along with Slowtwitch.com and eBay.  Remember you have to buy shoes and matching cleats.  I got my pedals for $35 with cleats and shoes for $60.   Buy your pedals first than look for compatible shoes (although a lot of shoes support multiple types of cleats).