the hoses all seem to be fine.... they get mildly warm when engine has warmed up but acqua temp still only gets to 90 whilst idling or sitting in traffic then resumes back to the 72point..... from car starting can take over 20 mins for the temp to rise above the 50mark... dammit alfa romeo *****... i really like you but you do my head in....
The top hose shouldn't get gradually warm....once the engine has warmed up the top hose should feel hotter and this happens the moment the stat opens. Did you hold your hand on the top hose throughout the whole test?
The 147 gauge does indeed work it's readings out differently to the 156 and other earlier Alfa's. Your gauge reading will never rise above 90 degrees unless there is an overheating issue. I've had two 147's, and driven several others, the gauge has never risen over 90 so yours is working correctly in this regard. However, once up to temp the gauge (working as it was intended to) should not drop from 90.
I'd do the stat test once more....keep your hand on the top hose all of the time, it's very evident if the stat is stuck open. If it's working, once the engine has idled for several minutes, you will feel a 'sudden' rush of heat through the pipe.
If the test shows the stat to be operating correctly, then I'd suggest to get the running temps checked through a diagnostic machine, but the temp fluctuation under the conditions that you describe are a classic sign of a perminantly open stat on the '147'.
It's more than feasible that your replacement stat is faulty.