Is there any advantage to paying for a tourist visa to Thailand if US citizens can enter visa-exempt for 60 days?

No

No advantage - I did everything once I arrived in Thailand

There's no advantage unless you want someone to pre-check and confirm your eligibility to enter as a tourist, which could be useful with excessive travel history to Thailand. Without that, no point getting a visa.

You can apply for a 90 days Non O retirement visa in country on both tourist visa (TM.86) and visa exemption (TM.87). You’ll need to get an agent to assist you with opening a bank account. I suggest you call your airline and ask about their policy regarding onward ticket if you plan to leave with a one way ticket.

The easiest thing is normally to apply for a regular 90 days Non at your embassy at home before you leave and do one year extension of stay in Thailand. Then you can just use your income/bank at home to fulfil the requirements, easily open a bank account and there’s no onward ticket requirement for regaining your flight.

Following, planning to visit Thailand for 2 months early November. Before travelling through South Asia untill November 2025 then Australia.

No point in paying for a tourist visa now really. Come visa exempt and you’ll get 60 days (plus 30 if you extend once).