RE: 2wd Slash vs HPI Blitz
I've driven a 2WD Slash offroad, didn't see what all the fuss was about. So I do have a little experience there (but not a ton).
As for grass - I guess it depends on where you live and what type of grass. In the USA, if it's grass near waterfront areas or lake communities, the grass tends to get a bit of sand in it, and it's quite scrubby and not all that lush - so that's easier to handle. In a place like my neighborhood, the grass is really thick, and it can be run through with a 1/10, but it's quite boring and the RC electronics get quite hot. Not sure what the grass is like in AUS where you're at - maybe it's easier to handle?
I've tried 1/10 buggies, 2WD and 4WD, STs, and even the Stampede 2WD with real grippy (not stock) Imex tires. The Pede did ok, but it still bogged down compared to dirt and got things hot.
A 2WD stock slash has less ground clearance than that, so in my lawn anyway, running it would be a boring waste of time with overheating electronics.