You'd have to spend A LOT to get much better than the Hartke. If necessary HPFs, cab sims and IRs can all be done "inside the box" in software for free. While a Tech21 VT bass will sound different, it's not necessarily better just a different flavour... and given Tech21's total lack of interest in controlling the cost of their products for anybody outside the US I wouldn't be buying one unless it's used. There's probably a cheap/free plugin out there that does a better Ampeg anyway if that's what you're after.
My only problem with the Hartke is its size, but since I'm not gigging it's not exactly a problem!