Was it a large store? A couple of the biggest stores in these parts have a reputation for trying to sell new bikes when they're really not needed. One woman I know who owns a very nice bike (about 10 or 12 years old, one of the earlier carbon fiber models). She went back to the store she bought the bike from because her chain was skipping, where they advised her that it was probably time to replace the bike and barring that the best thing they could do was replace the chain (which, if you know much about bikes, will NOT fix a chain skipping problem). Being a little tight on cash, she balked at that answer, and her next stop was our little community shop, where I diagnosed that it was, in fact, time for a new cassette. We biked 80km the next day, and it works beautifully. $20 vs $1000. I can see why the store wanted to sell her the bike.

A good bike store is about the long term relationship. Sell you shoes today (which probably have decent profit in themselves), and then a helmet next month, gloves the month after, etc. Evenutually, if you ever want a new bike, you'll probably buy it there. However, the larger stores tend towards commission based sales people who are only there for a few months. They don't care if you come back. This appears to be a successful model, but not the one I would choose to send my business to.

As long as there's nothing strange about your cranks that would prevent them from fitting a standard pedal thread, you're good. You may not have a performance machine, but that doesn't mean that you can't benefit from better pedalling efficiency. (Incidentally, you get more efficiency gains from the proper foot placement and lack of movement between your foot and your pedal. You don't get much out of the backstroke)