Advice for purchase of Southwest plane tix? Buy now or wait?

I’m looking at Vegas flights (from ABQ) in Oct for 4. Currently, $109 is the cheapest, which is obviously a decent deal by any standard, but the last flight tickets I bought included $36 tickets. Multiply that difference by 4 and it’s significant. Should I buy now or wait until I’m 3 months out (say) in the event there’s a sweet special in the meantime? Will Southwest let me swap fares if a better deal comes along?