I picked up a Miele past summer and did just that actually, used some shimano 600 8sp shifters I pulled outta the trash one night, swapped the rear derailleur to something that can index (an ultegra) and swapped the rear wheel, everything ran smoothly but I found the bike less fun to ride afterwords, guess those STI shifters are too convenient and lazy.
I cant imagine that rear derailleur on yours is original, looks like it came off a mountain bike, also whats with the drive side rear drop out, looks like it was broken and welded back on?
The Miele Binova was an upper entry level, sports touring model. Yours appears to be circa 1986/1987 and as such would have been originally equipped with a Shimano Light Action indexed shifting system.
If you want to upgrade to STI, I would suggest you try to find 7 speed shifters such as the Sora or RSX models. By restricting yourself to 7 speed you will not have to cold the frame for the wider spacing required for 8 or 9 speed and you will be able to utilize the existing hub/wheel The concern is that these shifters are harder to find than 8 or 9 speed. Also, while 7 speed, HyperGlide freewheels are readily available and inexpensive they have very limited choice in ratios.
Going 8 or 9 speed means cold setting the frame for wider 130mm spacing and buying a new wheel with a freehub to accept cassette cogs. The advantage is the parts are more readily available, a freehub is inherently stronger (i.e. less bent axles) but it is generally a much more expensive option, unless you find real bargains on used parts. Some peole will also tell you that you do not have to cold set the frame and can simply forces a wider hub into the rear triangle, however this is not recommeded.