I had a Mk1 1.2 before my old Valver - it was a much bigger step up than the Valver was to the Williams.
Youll probably know that a 16V can be a money-pit if you dont buy wisely, but there are very decent examples out there. My Valver cost a lot to run, but my Williams (which is a very similar car from a parts/repairs perspective) is spot on and has given me almost no grief.
My main advice would be to make sure that you have good cashflow every month if you want to buy an old hot hatch like the Valver. If it maxes you out to buy and insure a Valver, then its not a wise choice because there will be some fairly big bills along the way that you dont tend to get with a smaller engined car.
An "average" Valver with, say, 80k on the clock will probably give you a couple of £500 bills a year IMO. At some stage any 16V will need bits like the clutch, wheel bearings, rear arch rust, brake discs/pads/callipers etc. replacing - so it may be best to buy one with it all done.
If youre handy with the spanners or have ready access to cheap parts then this wont be a problem, but for the rest of us a Valver/Willy will have fairly high labour charges due to the small engine bay etc.
Id say that if you take care of your cars and could find a 16V in good condition, then youll have a bargain hot hatch that will make you smile every time you drive it. Theyre lovely cars that dont have the attitude or general air of rollox that a lot of the newer cars have - it a bona fide, old(ish) school, cut-the-crap hot hatch.
Id have no hesitation in buying another myself if ever I had to sell the Williams to raise some cash for something like a mortgage deposit.