Ray-

Unless you want to, don't go out and buy a whole new reel if you decide you need a 3 wt. line. Just buy an extra spool for either that 2 wt. or 4 wt reel that you have already, load it with backing and the new line, and swap it out for the existing spool when you're planning on fishing the 3 wt. rod. I do that a lot, as do many I'm sure. I have more rods than I do reels, the reason being that reels are typically rated for a range of line weights and it can be easy and much more cost effective to just utilize extra spools for multiple rods in the same range.