Large pool of addresses means more anonymous? how? For an average end-user, if bitcoin-qt is configured with a large pool (1 billion) of Bitcoin addresses, then will it increase user / transaction anonimity?
The pool of addresses is meant for consistency among offline backups. Not for anonymity. See: https://en.bitcoin.it/wiki/Key_pool

Generating and using a new address on-the-fly vs generating thousands in advance doesn't really make any difference in terms of anonymity. Just would create a lot of overhead.  What might help more is using a new address for each new transaction. Maybe.