intelligence points - spend or accummulate?

you use them per turn, but not using them is not possible.
if you don´t do any operations on other empires the intel is used to defend against other empires intel.
so it´s never unused.

In the Intel screen you can see a section named "Intel points reserved for defence"
If you don't 'spend' any that turn then they all get used for defence against enemy espionage attempts.

There is also the section estimating points used by other empires. This may be against you or other empires.

However, that estimate is not very accurate. If you play with player can see all scores enabled, the actual intel points can vary wildly. Estimate 213k against you (your generating 131k) Actual Intel 123k (combined intel of the 5 other races)

Watch the "defense successes" and "defense failures". If your failing to defend you will get messages, but you only get success messages, you don't get attempt failures messages.

You can turn on intel attacks, but you would have to overpower their defense points. This could leave you vulnerable to attacks.

I adjust mine to for as much attacks as I can (unless going for diplomacies) but preventing ALL attacks.