quote - I'd need a new rear wheel as well, of course, as the current freewheel is a 7-speed, but that's sort of the point; the cones are all pitted and it's a vain quest to keep the thing true - - and I'd never find a decent 7-speed road wheel, so to get a new wheel I pretty much have to take it all up to 9-speed.[/QUOTE]

why not buy some sora sti levers? they are available in 7 speed. You may find that you cannot fit a 9 speed rear wheel, as it may be too wide for your frames (rear spacing). The Tiagra/Sora shifters should work well with your existing derailleur.
Also, not that you can fit 8 and 7 speed cassettes on to a 9 speed wheel. You have to use a spacer for the 7 speed, but it works very well. Btw, for the price of the upgrade you mention, you could easily get a Campagnolo Xenon GROUP! Cheap wheelset (eg Vuelta) 60ukp. Xenon group 130 ukp = 190ukp to run 9 speed campagnolo, versus 110ukp for the Tiagra STI's alone....