I think I might be able to add some perspective to this since I played two years of NAIA ball back in the early 90's. Now as for D1 I have no clue because I didn't play there. There have been many changes as to how things are done so you may want to take things with a grain of salt.
Travel - NAIA may not travel as far as D1's but it's still an all day affair. We would get on the bus at 6 AM, drive 6 or 7 hours, play a game (sometimes two sevens), grab something to eat, drive 6 or 7 hours back to school and get home at midnight or later. We had to be in class the next day and we had to be at practice the next day. Sometimes when you start getting rainouts you might do this 2 or 3 times a week plus a home game. It will wear you out and make you hate life. I have no idea if that's worse or better than D1 but I know it wore me out.
Skill level - NAIA ball is vastly different. There are some schools that can compete with D1's and there are some that would lose to an adequate high school team. I saw and caught a lot of guys who threw high 80's and into the 90's but there is one difference from what I could see. A D1 pitcher will pretty much hit the spot the catcher throws up as a target most of the time. An NAIA pitcher will throw it just as hard but that area around the target gets much bigger in terms of accuracy. The off speed stuff isn't quite as sharp or breaks as much. They are pretty good but there's a reason why they didn't go D1. Hitters can hit but it just doesn't go as far or as hard as D1s. Another thing to realize is that admission requirements are easier at NAIA than D1 so you will find D1 talent at NAIA schools because they couldn't get into a D1 school.
Workouts - This is probably the one area where there might be a significant difference from D1. Obviously NAIA schools have less money than D1s so we never had any type of conditioning coach. Plus our coaches had to have other jobs to make a living. We had to work out on our own and there wasn't anybody to check up on us. Sadly this is the one area I wish I could go back and do over. I was always pretty strong and didn't work out as much as I should. During the season we didn't work out any but we did a lot of conditioning in the preseason and I mean a lot of conditioning.
Schedule - we played around 45 - 55 games I believe but I can't really remember now. We would play double headers on Saturday and if the team was relatively close during the week. Our typical week was something like Tue, Thu and Sat. Sometimes we would play on Sun but it was rare. We had some overnight trips but not very many.
Academics - when it didn't rain it wasn't too bad in missing class and we had to make sure we kept up with missed work. Obviously this was before the internet and mainstream use of computers. My freshman year it rained a lot and we had to move around a lot of games. I had a math class with another freshman and we probably missed two weeks of class. When we finally returned the professor didn't know who we were. We kept up with our class by getting assignments from others in class. We got through it but it was rough.
Overall college baseball is rough and you really got to want it to do it but it is something you will treasure the rest of your life. Some of my best friends in the world were my buddies on the team. I hope things have changed since I played but I would caution that if you play NAIA you need to have some self discipline to stay on top of working out and academics. You need it at any level but at the NAIA level you will probably be on your own much more than a D1.
NAIA isn't on the same level as D1 and never will be but it's still very competitive. You will find teams / players who fight and compete just as hard as D1 players. The wins are just as exhilarating and the losses are just as tough as you will find at the D1 level.