I think it is something about 1 GB ? am I right ?
The wallet is small, but the blockchain grows fast and will hit the 1GB barrier in a few months
The official client is fairly heavy on modern machines? am I right ?
It's not your "I never notice it" program, but not what I'd call heavy. Perhaps you have coin generating activated?
The fact is any data base design with no retention policy would some day (near) explode no matter what hardware new technologies exist.
Purging and a lightweight client is planned, but not available yet (afaik).
Do we need a new client with a built-in SQL database ?
I think Bitcoin uses Berkley-DB already
Do we need to create new policy to clean up aged blocks or transactions ?
See before, it's possible but not done.