True, I (almost) completely agree with jonatan. No reason to waste money, time, and energy to reach A3*S. This is actually true for *S in most of *A FFPs, although with some airlines *S can be useful when flying often that particular airline. SK for example offer to their *S additional luggage allowance, priority check-in, and (in certain periods of the year) access to SK lounges. But only when flying SK.

A3 though is far less generous. The only nontrivial benefit A3*S got was free seat preselection, but they were stripped of this a couple of months ago. So A3*S are only left with a couple of vouchers for class upgrade (useless unless you fly A3, and intra-European C for a couple of hours flight is not that a big thing anyway) and a few of tickets for the A3 lounges in ATH, SKG, and LCA (again useless if you don't use these airports, and anyway the quality of food and services offered in A3 lounges in ATH are imho subpar to most of the *A lounges I 've visited...).

When it comes to *A-wide benefits the only thing you get is priority in the waiting list, but this means you are still behind the airline's top/diamond/platinum members (for LH or SK for example), their own golds, other *A golds, and their own silvers. Could be useful in an emergency, but still a very long shot. So, I would advise against going after A3*S if you don't plan to get any further than that...