So I stay already for a few years on tourist visas with gaps of one to two months. My first ever visa from Vientiane ends soon. Should I rather fly to Cambodia for three, four days and enter on my first exemption ever or apply for back to back double entry visa in Vientiane? I would stay anyway just for two months before I need to go to Cambodia for one month. I could either use the first entry without extension or an exemption with extension and then applying for a visa after Cambodia.

You could do it either way.

It seems getting a visa exempt entry with a 30 day extension might be the easiest way.

Would a couple of days out be enough?

A couple of days would be more than enough.