Will this list also enable us to ask questions like:
Is it feasible finanacially to upgrade a Windows Vista or XP machine to Windows 7 so I can get the free upgrade to Windows 10?
Sure! You can certainly ask questions like that! And given the huge breadth of knowledge on FreeRepublic, you'll find you have the answer in fairly short order.
My opinion on your question: I haven't worked the numbers but if you can find a copy of Win7 Pro pretty cheap (and they are going for pretty cheap now that regular support has ended and it's on extended support, meaning no new features), my guess is that it's worth it.
In my opinion, Win 7 has it all over XP and Vista. XP was great for its time but it's wildly obsolete and insecure by comparison. And Vista was just a turkey. Win 7 came out real nice and works great -- that's what I'm running on all my production Windows boxes (other than testing systems). Win 10 looks to be another winner like 7.