To be totally honest.. the XXX BK1 is very similar to the new XXX-CR version.. probably a little stronger with the graphite than the new EA3 plastic. Basically the car you have is still at the same level...
As for your electronics... well.. if you have old NiMh packs.. then you will probably want to get new ones... A good well matched pack will be in line with a LiPo pack as long as you take care of it. If you have the gear to take care of a brushed motor (lathe.. etc..) you can still keep up. A well tuned 27t stock will keep up with a properly geared 17.5 brushless. It just takes more work to stay fast!
I'd say for mininal investment, you can get back into it!
Get out there and have fun!