As with most service recovery attempts, you are far more likely to benefit if you actually fly the airline more often than average. If you merely take the four flights to lower the Gold renewal threshold, then it's going to be more difficult for you to redeem the voucher at a time when base fares are high compared to someone who lives in Greece and relies on A3/OA's network far more - as KLouis' example illustrates.
It's not a con at all - just a limited opportunity - and certainly not something A3 has to offer given the voucher is given long before mandatory EC261 compensation would kick in.