What are the visa options for casual visitors to Thailand who plan to travel multiple times a year?

Get a tourist visa. Extend it once. Go back home and get another tourist visa. That will cover five months.

If you travel say 4 times a year, fly in/out, book hotels, have a return ticket home, thats fine on visa exempt. Its when you are trying to live here without a proper visa by taking your full visa exempt days (60 days) then extending (30 days) then doing a border run to start again. You will run into trouble. The Immigration officer will be looking to convince themselves that your either a real tourist or someone trying to stay without a visa.

No, you understood wrongly. They're not cracking down on casual tourists, rather on permanent tourists. If this is your first time in Thailand, you would have zero problems entering.

But how long will you stay each time, what country are you from, and will you try to extend your visa exemption each time?

The easiest is to get an annual visa for ฿1900 and a multi reentry permit.

If you are doing 60 days or less at anyone time you will be fine. Don’t overstay, don’t do border runs. I’m here now for the 4th time this year and I’ve had no bother.

If you treat the border runs like opportunities for a new visa only then yes you'll have problems.