$675 for a NIB parked Springfield Loaded is fair. It's a good gun too.
Springfield GI45s seem to be selling for $450 or so in park in my area.
Springfield Mil-Specs go for $500-550 in park here.
The extra money will not buy you a more accurate, or more reliable gun, but it will get you a beavertail grip safety, ambi thumb safety, nicer grips, forward slide serrations and a slide dovetailed front and rear for Novaks. If you want a swoopdedoo gun from the outset, it is cheaper to buy the Loaded than to make the Mil-Spec into a Loaded. Many people dislike forward slide serrations and therefore want the Mil-Spec to build up. Likewise, others want the vertical serrations and GI ejection port of the GI45.
I prefer Wilson magazines, 47D in particular. I order from
Brownells. You can occasionally pick up a few on a deal when someone sells a pistol. Buy the entire package, keep the mags, resell the pistol for what you have in it.
MIM parts have gotten a bad rap. A few parts on some fancy pistols that that were made in a place called Yonkers started to break, destoying a company's image in the eyes of many devotees. MIM has the potential to be very good, IF the manufacturer does not use it to scrimp and make a few extra bucks. Forged tool steel will always be superior. A quick search will prevent another MIM part flame fest.