Do you feel the 1.8L is a step up from the MR1?
IMO, they're not really a step up or down. More of a sideways move. Depends on what matters to you.
The MR-1s since they are higher revving, have a higher pitched sound that is really really bad. Really bad. The 1.8s are an annoying low drone. IMO, the MR-1s are only annoying once above 3k rpm but the 1.8s are always annoying especially depending on where you sit. Each is a very different sound and type of annoyance. The MR-1s cruising speed and above high pitch is way more annoying than the 1.8s low drone, but both still suck. The 1.8s cruising around at no wake speeds were fine if I was in the captains chair but if I was sitting at the very back, very annoying. The MR-1s sound problem is easier to deal with since they are higher pitched. Just sealing all the gaps makes a huge difference, but at the same time still annoying. The 1.8s are not as easy to attenuate. Nobody with either is really that happy even after extensive attempts to quiet them.
Fuel efficiency wise, they each have their good and bad. They're about the same at no-wake speeds, the MR-1s are more efficient at cruising speeds, and the 1.8s are more efficient at higher speeds to WOT. The MR-1 boats have a much longer range if you stick to cruising speeds.
One big issue with both is the engines are hard to control throttle wise if you want to pick a speed just above no-wake, but below cruising. Very little throttle movement causes the engines to jump in rpms. So Yamaha gave us an "amazing feature" called no wake mode. You have some buttons for easier speed control. The MR-1s only offer one speed, the 1.8s offer 3 speeds. This feature is really a band-aid for the lousy throttles. Imagine pulling into a parking lot and not being able to use your accelerator and needing to switch to some buttons, would you call that a feature? What if they just made the accelerator work properly for all speeds?
For me, personally, I prefer the MR-1s. Riding on my boat that I've done work to quiet vs riding on a 240 with no sound mods, I pick the sound of my "quieted" MR-1s to the factory 1.8s. I also appreciate the MR-1s having a further range and being more fuel efficient at my most common crusing speed. I do wish I had a throttle that worked properly or at least the 3 speed version of no wake.