The thing about Apple is even if M3 brings a 30% lift in efficiency and battery life then Apple will reduce the battery capacity to match and keep the specs in line with current MacBook air.
The M3 will likely have a 30% lift in GPU performance if past iterations hold true for reference and we might see a 20% or better improvement to CPU performance. It should definitely be better than M1 to M2 but again Apple can adjust so many parameters to keep a predictable performance boost and then next gen M4 will probably be an optimization of M3 just like M2 was an optimization of M1.
In this way they are sticking to the tick tock updates that Intel used to do but in Apple terms. It gives people a predictable performance time line and makes generation to generation upgrades not as important but wait a couple generations and the difference is significant. This is a smart strategy because if they did huge performance upgrades every year it would start to devalue Mac resale value which has been traditionally much better than the PC market.
So if you get a M2 MBA 13" or 15" you can still enjoy it for years to come. What I wouldn't do is buy an M1 since it is getting a bit older now. However even regular M1 is still a fantastic chip for everyday computing and M1 Pro is still a very good chip. I have a feeling that Apple may support their own Mac CPU chips longer than in the past with Power PC and Intel. I could be wrong but it would increase the value and longevity of a Mac and would be another selling point that wouldn't really cost them much money since they are developing on the same architecture and CPU. I am not sure if the M series chips have arm v8 still but the switch to v9 might be the only thing that might be an issue but I honestly think I may have been wrong in writing off M1 in the past as being old.
M series chips have a much different potential in support than any previous Mac's and M1 is still very fast and efficient. So they may be around and supported a lot longer than previous CPU Apple has used.
So all of my talk about M1 being old was due to my perception and experience in the past and I may have been wrong to extrapolate that to the future.
So buying an M2 Mac should be fine even if M3 is introduced tomorrow which we all know won't happen for Mac's.