Follow-up: I did a bit of a cross-over analysis, taking my Vaio to another wireless router and my MS Surface Pro to this one at home (where I am having the connectivity issues). I note that I had drops with the tablet also, albeit briefer, so perhaps it is (was) more of a router phenomenon.
Further, the router started to experience acute base (non-wireless) connectivity issues a few days ago with the DSLAM. So...
I went to my ISP and swapped out the old Zhone router for a new one (Zhone Model 6729-W1-NA-0CC) and thus far all is well. Will let you know if I have the issue as before.
Conclusion: perhaps it was [inexplicably] the router all along...
Joseph