I have had two 3720 tractors, and have been pretty happy with both of them. Both were the open station machines as I do not have an indoor place to store a cab tractor. I have previously been a "get the biggest or most powerful machine" in a given class, but have matured a bit from that. I also have more experience in these machines and have found similar findings to those initially noted. The 3720 is a nice tractor, but it really will not outwork a 3520. I can think of no instance where the extra power of a 3720 really makes a difference except in all day super high load PTO work, which really none of us do that much--if at all. John Deere, being a smart company, has marketed these high horsepower machines as being a smaller alternative to the next larger series and people have gone for it. When I bought my first 3720, I priced it quite close to a 4120, but still went with the higher HP 3720. After I had owned a 4520 and used a 4120, I realized the 4000 series are certainly more capable and really should have been my choice previously at the time. The same applies IMO with the 2020 to 3020 jump. The more powerful 2020 machines approach the price of the lower 3000 series machines, but are not as heavy duty. The short of this is that if one is looking for the best deal possible, it is often better to look one model below the flagship in each of the JD lines. These machines often are quite a bit less pricey, opening up saving money v. getting an extra attachment or some extra features and the actual real world performance is essentially nil. My personal example of this is the first 3720 I had v the 4310 I had prior. In pulling a 72" RFM mowing a large field I found the 3720 to have no trouble mowing very deep, thick grass. It would, in fact, pull the mower so well one could smell the belt burning. The RPM's never changed. The 4310, pulling the same mower but with 10 less PTO HP (same physical size) would do----the exact same thing. No bog, belt smell, whole thing....This attuned me to the fact that extra power is helpful, but frequently more is a bragging right than a true performance enhancer, especially when the numbers are close and especially when dealing with turbocharged machines such as the 3520 and 3720.
John M