Situation in my last home tourney.. what would you do?

Blinds were 75/150.

15 still left in tourney, top 5 pay.

My table had 8 people.

Everyone folds to me, the button:

Button Hero: 750
SB Player: 1,500
BB Player: 3,000

I get A-4s (clubs) on the button.

To give you a history, when the blinds were 50/100, I was SB with 7-7 and raised to 400 and the BB (Player 1 up there) went all in. After deliberation I folded and he showed K-K. So I admit in this new hand I'm discussing I was a bit timid to raise...which cost me.

I call 150. SB and BB call and check.

Flop comes 6-4-Q

SB and BB check. I smell weakness and go all in for my remaining 600. SB calls with a Q-8.

In retrospect, I do think I should have moved all in with A-4s but I was overly cautious. I think I played it correctly given my mistake, he just happened to slow play the Q.

Any thoughts would be appreciated.