If purchased directly from Apple, you have a generous 14-day window within which to unconditionally return your device for exchange or refund. After 14-days, this opportunity is lost.
After release of a replacement model to general sale, your current model iPad may become eligible for Apple’s trade-in programme - but the value that may be offered will be significantly less than you paid for your existing iPad. You are likely to achieve a higher value of you sell privately.
Apple Trade In - Apple
Consider that the latest model model iPad Air offers an incremental update. Unless you are running “benchmark” Apps, or are using the iPad for particularly intensive tasks, in practice you are unlikely to notice a significant difference in system performance.
Chasing the latest and greatest at every product iteration is an expensive pastime. Unless you have pressing need for a more powerful iPad, perhaps enjoy the iPad in which you have already made investment - and in a few years, when the difference is sufficiently obvious, it is then that replacement might be considered.
I hope this information and insight proves to be helpful to you.