It depends on your style, but I think it is fairly neutral EV to add on at the start.
For me it is a matter of how serious I am about the tourney.
I usually play rebuys to blow off steam and I may not be playing well and just want to quit after my first bust.
Sometimes I take the max addon sometimes I skip it. I have had great success both ways (mind you this in only in the $1 rebuys on UB but I have made over 1600 in them).
My personal philosophy is that you should not play any differently in a rebuy tourney than a regular tourney. You should always take +$EV spots for all your chips.
But you must recognize that your opponents may be much looser in a rebuy so calling a 3 way allin with 10 10 may be plus $ EV (I have done this in one before and quadrupled my stack).
Adding on will double your chances up winning, but it is also doubling your buyin, so I think it is a wash.
If I bust later in a rebuy tourney and decide to play on I will definitely add on to keep up with the increasing blinds. If I can buy in for 50bbs instead of 25 I think this improves my odds
because I won't be as rushed.