I can wait, although I would to benefit from the faster shooting either of those cameras would offer. I am planning to shoot a lot of high school sports starting next summer
You are upgrading from one entry level camera to another. Yes, there are some definite improvements from the D3000 to the D5100, but if you do that you will be back here in 6 months, a year TOPS wanting to upgrade from that... That's a lot of wasting money and upgrading. If you are going to upgrade out of an entry level camera make sure it's an UPWARDS move.
If you are planning on shooting high school sports indoors in any gym or on a night light football field you are better served by upgrading lenses. You will NEED to have f/2.8 lenses in any high school gym and on any football field at night or neither the D5100 nor the D3000 is going to do much of anything for you. Your images will be underexposed using anything other than your 50mm and you will quickly find that it is pretty OK for something like volleyball, but for basketball or football? It's WAY too short and you NEED the zoom. At f/5.6 on your zoom end? Your shots won't be usable because they are underexposed and raising the exposure will cause noise issues you can't fix.