Well, I did it. I changed plans at the last second, though,
going for the Hustler CG-144 monobander with radial kit.
Instead of paying $200 for the GP-9, I paid $27 and got
almost as much gain.

After figuring my old antenna's gain - coax - connectors, I
figured the new coax (Flexi 4XL) and antenna. The new
antenna is 5 feet higher and my system gained 3.940 db.

My S-meter on my 2 meter rig is stingy, esp. around S8
where it has an almost logritmic scale action. Still, several
repeaters went from S3 to S5 and several went from S7
to S9. One repeater remained S1 but it's noise factor went
from 50% quieting to 70% quieting.

Turns out it probably was a good decision - the Hustler
has 5.2 dbi gain and the tip is at 42'. I'm just stating to get
intermod at this level of performance (I live between a
hospital & Boeing). I'm convinced if I had gone with the
GP-9, I would have serious intermod problems (plus my
wallet would be $170 lighter) plus raising it would have
been MUCH harder.

The worth it question seems to be that you spent $ 27 for a net gain to get
one repeater to go from about 50% to 70 % quieting. The other repeaters
were peobably full quieting so you would not gain anything on them even if
you spent the full $ 200. Whe 'worth it " will come when you are making
contacts that you did not make with what you already had.