Question about add-on decisions

[feelixthegreek]

At my local B&M I play in a weekly $50+$15+$5 tourney with one $50 rebuy/add-on during the first hour (the xtra $5 gets you an additional T1000 up front). We begin with T2500 with blinds at $25-$50. It's not a very good structure, but leaving aside that for a moment, I'm wondering when it is worth/not worth taking the T2000 add-on at the end of the first hour. After the add-on period, the blinds are 100-200 with a 25 ante.

How few or how many chips makes taking the add-on a bad play? Or is it better strategy to take the add-on immediately at the start of the tourney?

Maybe my questions aren't clear (or maybe the structure of the toruney renders this concern pointless), but the bottom line question is when is it not worth investing an extra $50 into the tournament because you're already too weak or too strong for it to have an appreciable effect on your chances?