I have a 3,000ish song library (growing all the time), but I bought a 16GB iPhone 4S. I thought that I wouldn't need all my music on there, opting to not sync a lot of my music. However, I still ended up with like 10.5GB of music, which doesn't really leave me much room for apps/videos/pictures. Therefore, iTunes Match is a no-brainer.
Also, $50 for 2 years (assuming you have your 4S for only that long before upgrading) is cheaper than getting a 32 or 64 GB iPhone. Hooray for saving money.
Also, $50 for 2 years (assuming you have your 4S for only that long before upgrading) is cheaper than getting a 32 or 64 GB iPhone. Hooray for saving money.