First of all, I wouldn't trade the Python.
I think whatever role you're looking to fill with the Glock is already filled (better, IMO) by the XDM. If you really want a .357Sig, you could trade in the XDM and get an XD in .357Sig. The improvements of the XDM over the XD are pretty slight.
IMO, XDs/XDMs are absolutely as durable and reliable as Glocks, while being more comfortable (your milage may vary).
Actually, if your Python is worth "at least" $1000, buying an XD in .357Sig without trading anything would cost you about the same as trading a 1K gun for a $550 gun. And you'd still have your wheel gun.
At any rate, I don't think I'd make a trade like this guy wants -- you'd be down a good bit of money. Less money = less guns.