When getting plastic cards for personal use, never assume that purchasing replacement cards is a viable option. They're a different color from a card thats been aged and used a bit, so a replacement card is as good as marked. Keep in mind that a good poker player can use the placement of any single card in a deck to great advantage.
This isn't the case where there are tons of decks in use at a 50 table duplicate bridge match, where everyone uses each deck once.
Plastic cards are fairly useless for mechanics, unless they've practiced with them a bunch. In a poker game where you're likely to meet one of those guys, hopefully you'll be using new decks with high frequency anyway.