than the frame. Low SHGC glass does the most on the west-facing bay, where afternoon sun is what makes rooms hard to cool, and a low U-factor keeps the rooms near the windows from feeling cold and drafty in winter. Foam-filled frames and better spacers do less for the bill but reduce drafts and condensation at the edges, which is what you feel when you sit near a window. Before paying for the upgrade on all 37, have an installer or energy auditor check which rooms actually have a heat or cold problem, and consider high-performance glass on the west and south exposures with standard glass on shaded sides. Ask each installer for the NFRC label on the exact options so you can compare the numbers for your windows.

" My question: how much is it really worth paying for the pella window upgrades such as foam or advanced comfort plus or sundefense, etc "

The correct glass package is paramount. That being said are you 100% sold on Pella as you can do much better? Personally I would leave what I had before purchasing Pella but that is me.