Using spaghetti squash for ‘pasta’

One simple change you could make is to simply not mix the squash with the sauce, instead, plate the squash and then pour sauce over the top, the sauce will cool quicker which will reduce the amount that the squash cooks past the point you decided that it was ready.

If the squash still cooks too much on the plate, try starting your sauce earlier and letting it cool so it's warm but not scalding when served.

I wouldn't recommend just taking the squash out before it's done and letting it finish in the sauce, since as it's cooking, it releases water, which would be lost in the oven, but would thin the sauce if it's cooking in the sauce pan.

If you need mix it with the sauce before serving, let the sauce cool to the point where it won't cook the squash further before doing so.

There is a legal difference: according to Italian law, pasta (which includes spaghetti) is made only with durum wheat. Other countries also accept soft wheat. The difference is in the amount of protein (mostly gluten): durum wheat has more, which in turn gives the pasta a somewhat snappier bite. Also, the cooked pasta stays eatable (as in, non-mushy) for a longer time.

Moreover, some Italian pastas are extruded through traditional bronze dies that leave a slightly rougher surface that makes for better sauce adhesion.

Avoid by all means all stupid Italian pastas made for tourists. Avoid stupid novelty shapes and (most) colored pastas. Some good brands with global distribution that will not let you down: Barilla, Agnesi, Garofalo, De Cecco (thanks for the tip).