if you forgo the $400 every two years for the Aspire upgrade and figure on the normal subscription rate of $500 per year
for Fusion the numbers even up somewhat.
Sure, but that's like saying a 1970 Corvette is a better deal than a 2019 model.
Fusion is updated constantly, so you'll always have the current version.
If you don't update Aspire, you only have what you got when you bought it. Having said that, if you don't need any of the newer features in an Aspire update, then there's no reason to pay for the update. You can skip as many as you want, and still just pay the $400 for the upgrade, even if you are jumping forward 3-4 versions.
For mechanial or engineering type work, 100% Fusion 360.
Fusion 360 is a full parametric modeler, and it's integrated CAM can create toolpaths from features, surfaces, faces, or edges of the model, as well as from 2D sketches. Fusion also has a TON of other features, including assemblies, rendering, simulations, ...
And Fusion has a variety of toolpaths that you'll likely never see in Aspire.
Aspire was designed to create 3D relief models. It's native format is a pixel based "height map". Models have no features, and your toolpaths are limited to simple roughing and finishing parallel paths.
Fwiw, I'm an Aspire beta tester.
Here's a Fusion 360 model of the new router I'm building. You can't do anything like this is Aspire.