How can I access my 37,000 photos in iPhoto now that this "upgrade" has screwed me over????

64 bit Photos replaced 32 bit iPhoto.

Launch Photos with the option key held down. Point it to your iPhoto Library and Photos will create a new library with your iPhoto Media.

It really is nothing personal. It's just that you didn't check to see the consequences of upgrading. If you had you'd have saved yourself a fright.

iPhoto was discontinued 6 years ago. It is no longer developed or sold. It was replaced by the more powerful (and free) Photos.app that comes with the OS. You can migrate to that app very simply:

Hold down the option (or alt) key and launch Photos. From the resulting menu select 'Choose Library' and point at your iPhoto Library. It will do the rest.

If you prefer not to use Photos there are several 3rd party apps that you can use. Which to choose depends on the kind of photographer you are and your budget.