Ismael Jones is a well respected Minelab modder & states that in his opinion there is no need to mod a GPX model. For a modder to say that well that says it all to me. I wouldn't do it to a GPX on the back of that + they are still serviceable at Minelab unmodded if anything should go wrong down the track. Modded they aren't.
Heres a write up by Ismael with some points to consider:
http://www.minelabmods.com/joomla3/
Also a lot of people believe their modded machines are worth more but if you ask anyone that has tried to sell one you might hear a different story - I know one past member here had a hard time selling one. Dealers will also not take them for trade ins etc.
I think it's a matter of personal choice but it needs to be weighed up beforehand. I'd probably want to test drive a modded one first & have some guarantee if they don't live up to the modders claims.
As Heatho suggests - try one of the new coils first. They might put enough spark back into the 4500 at less cost & risk assuming that the 4500 is still worth something to you?
