Is partial double glazing worthwhile

Thermal insulation (and a vapor barrier) is applied between the interior and exterior surfaces of the home. Unless you plan on leaving your basement unheated, you wouldn't place thermal insulation between the floors. And leaving it completely unheated is a bad idea since pipes can freeze.

The only reasons to place insulation between floors is for sound or to slow the spread of fire. For fire protection, the places you'd install insulation are where fire could spread up an opening like a chase for running duct work and other utility lines.

What's left is sound protection, and that is best provided by using flooring materials like carpeting above, and then separating the drywall from the joists with something like resilient channel. Insulation in the ceiling cavity will only reduce the high frequency sounds from above. The low frequency sounds, such as loud footsteps, will travel directly through the flooring, the joists, and be rebroadcast by the drywall. Think of sound like electricity, the joists as a short, and carpeting and resilient channel as tools to prevent that short.

This is hard to do and I agree that there is a big range of cost between basic insulated sealed units and some of the high performance glass units which can be triple the cost. Here in Canada when we install a commercial glass project we are required to provide warranty documentation from the glass supplier which shows the makeup of the sealed units ( glass thickness, low-e coatings and any gas filling details ). This information even provides the invoice numbers for glass provided for the job and can be a great help in matching up replacement glass when breakage or insulated glass failure becomes an issue down the road. I would try to get this documentation from window / glazing contractor. If this is not available there is a measuring tool from CR Laurence that can tell you the glass thicknesses, airspace thickness and what surface the low-e coating is on. It won't tell you the type of low-e glass nor whether there is any argon gas but will provide you with basic information. A professional glazier can often take a look at the colour of the glass from inside and outside to point you in the right glass type direction as well. Good luck!