I have done a 3 tank day trip. We began the morning at Between 2 Buns just after they opened and grabbed sandwiches that we put in a cooler in order to have some food for the day. Also carried plenty of water. We were able to do 3 dives pretty easily and be out of the park with plenty of time to spare and got in a 4th sunset dive back out our house reef. However, we chose to not go to the furthest north spots (Boka Bartol, Playa Benge...) and instead went to Wayaka 2 for two dives and Boka Slagbaai. This does save considerable drive time.
My takeaways:
1. It is really pretty and a very different experience
2. It is isolated. So, if you have car problems, an accident or dive related issue-- it could be very problematic
3. We were the only ones diving on those dives. Total solitude! But, that can also be had outside the national park
4. Weather and currents can be unpredictable and could potentially turn the day into a "bust"
5. We thought the dives at Wayaka were quite good and better than Slagbaai. Slagbaai is a truly great beach and wonderful setting though
6. I have not been back since. It was fun to do, glad I did it, but don't plan to return. It makes for a very long day and a ton of driving. If the diving experience was markedly better than other dive sites more easily reachable and safer, then I would return. But, in my opinion, they aren't and don't warrant the additional effort.
7. I have considered going back on an "off-gas" day. My flights return early Sunday mornings, so the last Saturday is a complete no dive day. It might be nice to take that day and do a leisurely drive through the park, pack a picnic, do some snorkeling, etc.. I'd rather do that than give up a dive day at dive sites much easier accessible.
8. There is no additional cost to enter the park if you keep and show the ticket that comes with your annual marine park pass.
Given the amount of Bonaire diving you are doing, I'd probably encourage you to go for it-- Do a 2 tank trip and see how you feel about it. Just keep in mind the potential hazards of the isolation. Self sufficiency is paramount.