If you return your 3570K more than likely you're going to incur a restocking fee, typically 15% or more. So the net cost of the 3770K will be substantially higher that your original 3570K purchase.
Some forum posters say the 3770K is binned higher than the 3570Ks but I haven't seen any real proof. Many if not most of the high overclocks on the 3770K are with HT disabled, which puts both chips on very nearly equal terms of performance, certainly not noticeable in daily use. The 3770K's extra 2mb of L3 cache is nice but makes little difference unless you're using highly specialized applications that really take advantage of it.
Before I purchased my 3570K I was really considering a 3770K because I do a fair amount of video editing, conversion and transcoding but thought that I'd rather put the extra cash towards a better video card and utilize Intel's QuickSync for the editing instead.