Lychee in Fang no longer producing well. What next? Lamyai?

We have had several warm and wet years in the Fang valley and our lychee trees have not been producing well without the cold snap they need. We are at 500 meters and our neighbors are having the same problems. Many say this is going to continue and are now focusing on longan.

We already have 10+ rai of longan and I am not sure if I want to plant more longan as I like to diversify. Also we know how to work with lychee and it used to make a lot of money.

We are preparing another 8 rai to expand our orchard and had planned to air-layer new lychee trees to fill this plot in the coming months. Now I am not so sure if we should plant more lychee. There is a new lychee cultivar being sold but it is very expensive (150 baht / tree) and i have no evidence that it will do any better than the current cultivar.

We have oranges and mangoes but they are too labor and capital intensive for us to plant more right now. And for other reasons we are not so interested in corn, cassava, etc.

Should we shift away from lychee and plant longan instead? Should I believe the gossip that lychee are becoming long-term losers in our area? I am worried we are just following the herd and longan prices will plummet once ours come to maturity. Or the supposed 10 year trend of worsening lychee yields (of which I have only personally observed 3 years) will reverse.