Going from 9-speed to 10-speed requires new shifters (the most expensive part), a new cassette and a new chain and possibly a new front derailleur. About all you can retain are your wheels, crank and rear derailleur.

I have no idea how the first "tech" at Nashbar could have given you such bad information.

Edit: I just noticed your 11-speed question. Yes, along with the the shifters, cassette chain and front derailleur you will need a new rear wheel to accept the wider 11-speed cassette and probably brakes to match the different cable pull. I'm not even sure the older Shimano 7/8/9/10-speed compatible rear derailleurs work with 11-speed. This is going to be a costly update, even if you do the work your self and a lot worse if you pay the shop to do it.