But I have to wonder, at what point does it really make sense to replace my windows?
There are many possible reasons for replacing windows; energy-efficiency in a brutally cold climate is only one of them. Only you can decide if it's time to replacement them. Even in a warm climate, you may wish to replace them for any combination of the following:
1. Existing windows are difficult to operate, won't open, or stick
2. Better sound attenuation (Oberon, that means noise reduction)
3. Peeling paint/get low maintenance on exterior
4. Rotted wood
5. Missing parts
6. Damaged glass or screens or poorly fitting screens
7. Poor performance: worn weatherstrip, air/water infiltration, drafty
8. Ability to wash windows from the inside
9. Warmer more efficient window in Winter (for cold climates) or better heat blocker (for warm climates)
10. Resale value
11. Appearance - clean, new, low maintenance look, possibly different color or style
13. A new look - such as bigger windows, a bay window, a patio door, arched windows, divided lites, more light in a darker room, etc.
If people replaced windows for energy efficiency alone there would be a lot less windows replaced. Replacing windows is not only a home improvement, it can also be a lifestyle change.
The above addresses "should I replace," and again the answer is "That's up to you and your reasons and motivations." The 2nd issue, "Should I use high-end products in a warm-weather climate," that's hard to say. I'd prefer "Yes" to higher end brands
(but without the high end options), because they work the way they're supposed to and presumably have good service to back them up. But you wouldn't need high-end bells and whistles, such as triple glazing. A lot more could be said on that issue, hopefully others will jump in.