I might be interested, save for there's little in the tech tree to begin with and even less I don't already own. I'd trade in the 50% off TOG or SU-100Y I purchased years ago and never used for something, except the only tanks I'm interested in (M46 KR, AMX 13 57, Mutant, or 252U) aren't generally available.
Also only getting 50% feels kind of cheap, though I guess it's that way to prevent people from buying something on a 50% discount and trading it in for 75% of full price or somesuch.