I'd rather swap discs than pay $20-30, but then it would only cost me 1/4/th that currently due to sharing. However, the potential loss isn't that great. Sharers would still have to buy instruments; and perhaps code the export to only work with RB2, therefore forcing them to buy that game, at least. I think that would work nicely.
But whatever, if I have to swap discs for a few songs that I'm not tired of by that point, then so be it. I love that the DLC will be compatible.
I love that for GH4/GH3 DLC as well, because most likely I'll end up wanting to buy that game and getting some GH3 DLC I've missed out on. 2 sets of instruments and 2 DDR pads is really going to get crowded...