The short answer is probably "Yes, but not much". For the average motorbicycler (are any of us really average) there won't be much noticeable difference in higher quality parts, but those who ride a lot can tell the difference.
For tires I am partial to the Electra Retrorunners myself. They have a nice profile and give a nice ride. I also like the 8-ball logo on the sides. I like them so much I sent away to England for a set with red stripes on the side (no longer made) and I have a white wall set on another of my bikes. These tires run about $40 per tire, but I just put a set of Cheng Shin
tires ($8.50 each) on one of my son's bikes and I think those are pretty darn good too.
People of a more rounded physique (hey, ROUND IS a shape!) should probably be more concerned with the spokes than the bearings as the bearings are generally over engineered anyway. I'm a slight bit (and I am being generous to myself) over your 245 and I had the rear spokes fail on my main MB. It now has thick, 14g spokes on it.
I can say this. I have four of these motorbikes now. Two of which are built on higher quality frames and two on less expensive frames. The best bike by far is the first one I built which is on a $400 Electra Coaster 7d frame. The ride is perfect and the bike is very solid. The next would have to be on the Grubee GT2 frame which is about the same price category. But the ride on these two is only slightly better than the ride on my $150 Greenline BC-106m frame.
The fourth bike is on an old AMF Roadmaster frame and the ride suffers more because of the narrow tires than the frame itself. Since your mountain bike likely has nice fat tires on it, you won't have much of an issue.
For your situation I'd recommend maybe getting a set of smooth tires to replace those knobbies on the mountain bike (assuming they came with those) and maybe start setting aside some money for new rims later just in case.