I'm usually cackhanded too, but I'll be honest I found this pretty easy, the only risky bit is removing and handling the drivers. Everything else is easy.
I'd do it again no problem.
I think even just adding the extra bracing and acoustic foam made a big difference, you could tell right away when you tapped your knuckles on the cabinets before and after. So I would say that a cheap and easy upgrade would be that on it's own. Obviously doing the crossovers can be done at different levels too, whether it be a recapping or full blown replacement I'm pretty sure each level would bring improvements, albeit incremental to whatever level you chose.
For the cabinets I bought 24 x 30cm square wedge shaped acoustic foam - £28 inc delivery. 20 Sheets of 2mm Silent Coat - £45 inc delivery and a 2.4m length of 50mm x 18mm softwood strapping - £3.30 from Homebase. So for around £80 I'm sure you would hear improvements