Is this a Crazy Plan?
 

We are planning a trip in a few months, but unfortunately the available quality redemptions right now for places we want to go are few and far between. However, just doing a bunch of close-in searching reveals a plethora of options as we don't really have a firm destination set in mind, so the thought occurred to me that we should just wait until we are a couple weeks out and start looking for good options to travel from essentially NYC area to anywhere that peaks our interest and has a good redemption for business or first, then figure out accommodations, etc. While at our destination we would figure out the return flight and, possibly, book a cheap repositioning flight to get to the return flight. For example, it looks like there are several days next week with LH 1st award space from JFK-FRA so we could theoretically transfer chase/amex to aeroplan to book, find some EU hotels or airbnbs in various locations and train it between where we are staying (since we like to take trains around Europe, generally). While there, we could keep an eye on return flights to the US west coast and book the return flight and any repositioning flights on either end. I think this is totally doable but my wife, who likes everything planned in advance, has doubts. I think that with a load of flexible miles (chase/amex) this plan is easy to execute and low risk. Does anyone have similar experience doing something like this? I would be curious of anyone who has tried this and hit a snag.

Not unreasonable at all. If you already have points with an airline who doesn't charge for a cancellation (e.g AA,UA) you could consider booking something as a placeholder and then just keep watch to see if something better comes up. With Chase and Amex to transfer, you have many options, though I wouldn't suggest transferring points until you are committed otherwise you are stuck with that one airline.

I've done this several times with very good results. If you avoid peak school holidays and major events you can do extremely well. The only issue might be high speed trains (if you plan on taking those) - those tickets start out cheap and tend to rise over time. Some trains sell out.

For low season it is the (only) way to go; much cheaper and better options this way + the flexibility.

I second the comments about train tickets in Europe. They only get more expensive as you get closer to departure.

The only thing I would really want to do is take the Glacier Express from Zermatt to St. Moritz in Excellence Class. It looks like that might be a harder ticket to book so I may gamble on that and buy farther out and just assume I'll be able to get to the EU at some point before the departure date. I have been looking close in right now and it looks like there are a ton of options on almost any day within the next week to get a nice redemption to somewhere close. I assume that will probably continue after the summer high season.

Thanks everyone for your input!