I may be a bit late to this thread, however, MPLS is my home airport, Delta is my primary airline and AMS is usually my gateway airport, so I will chime in nonetheless. One other option is to simply wait. Taking the time to analyze when to use your earned Skymiles effectively can lead to ulcers. I understand getting your trip booked straight away checks off one thing from your vacation "To-Do" list, however, by waiting, you may very well secure that direct flight home from AMS to MSP in July for an low Skymile amount. I tend to hold onto my miles and wait to book flights to Europe when the value of the flight I want appeals to me, much as what you are attempting. Currently, in my view, Skymiles to Europe are a pretty good value in the Main Cabin, but using Skymiles for First Class has been a terrible value in the last year or so. So, waiting for the price of Skymiles for the flight is a good option. One thing you can do to stay on top of this is when you are searching for a flight you want, start the booking process and see the seats available in the Main cabin for the flight home you are interested in. If most seats are available, that is usually a good sign that pricing will come down at some point (However, some rumors are out there that airlines manipulate their seat map to have potential customers think they are close to being full).
Also, please be advised that Delta does fly direct MSP to KEF (Iceland) seasonally. On two occasions, we booked a cheap flight from Europe to KEF (flights can be as low a $59 on Iceland Air or other budget airlines) and did our own planned Iceland stop over for a night or so, then flew home from KEF to MSP on Delta. I find flights to and from MSP/KEF to be cheaper and of more value than AMS, CDG or London.
Last, I will pass along something I learned on one such trip which was a lesson learned. I sometimes book two separate one way trips to AMS on Delta for various reasons. Delta has their own extra security step at AMS (all Delta flyers to the US have an extra line up of security at gate D1). On your way back home, they will want to know how and when you arrived in Europe as they will not have access to your ticket information for your one way ticket to AMS. So, make sure you save a copy of your flight from MSP to AMS on American in your backpack as I promise you they will want to see that when you try to head home. I always do that now as I failed to have a copy readily available and it led for a rather lengthy delay to find it on my smartphone to show the Delta agents.