Nah... one of my SDIs has been parked up since march. I've probably done only about 200 miles since then in one of them. Had to go out for it's MOT in August, but other than that I only take it round the block once every couple of weeks just to keep the brakes clean and keep the cobwebs away.
I get trade price on my MOT from Halfords in Tilehurst for just £24 as I help them out occasionally on clients' electrical problems, so my main cost is insurance at about £20 a month. Plus tax at £30 a year. Running costs are almost negligible now, as spare parts prices are on clearance everywhere, and as we all know you need to walk if you want to find a cheaper way to get from A to B...
my ratings for a Lupo SDI:
running costs 10
fuel economy 10
compact convenience, parking etc 10
comfort 2
reliability 9
street cred 4 (and rising)
depreciation 10 (prices have hit bottom- possibily rising! As they're now becoming more desirable)
Makes sense to have an SDI on hand just in case...