...The biggest size I usually print is about 16"x48" or 24"x48"...
As an aside, I've been selling bigger prints, landscapes, 20"x60" made with a 10 Mpx camera. Emotional impact, not tiniest of details, sells pictures. Having said that, however, I visited your site (nice pics, btw) and your images do benefit from a photographic veracity, i.e. fine detail. Just how that translates into $$$ is the real question.
If I were you, before spending $45K, I would...
1. Assess your market. You said it is a tourist area. $45K would give you more or less the same level of detail, but in much larger print sizes. The question is, is your tourist crowd the type that would pay significantly more for larger sizes? Otherwise, if you just get photographically "better" prints at sizes you currently sell, would clients notice the quality difference, and if they do, would they care? I'd say the benefit of MFDB would be in larger print sizes, but do you have a market for that?
2. Shopping malls and tourist markets do not seem the type of venue that would cater to the high-end buyers, the type you'd need if you'd want to recoup your investment reasonably quickly. A bit more luxurious gallery would be needed. Again, would you have the crowd for that? In the States, most photographers who sell in millions (US$) have galleries in major posh tourist areas: Las Vegas, Jackson Hole, La Jolla (San Diego). Even then, not all shoot with expensive equipment. Peter Lik does shoot today with expensive MFDBs, but his success is predominantly based on marketing and selling skills. Thomas Mangelsen, however, made his millions with a 35mm Nikon, shooting wildlife and landscape, producing successful huge prints, on occasion, with digital noise or film grain the size of golf balls.
3. Determine how aggressive and ambitious are your marketing and selling skills. If you are the type of photographer who would rather gauge his eyes with a plastic spoon then engage in a horse trading, bs-ing, and second-hand car salesman techniques with a customer, find someone with those skills to do it for you (more cost, however).
4. Not place too much expectation on potential online sales. For that, you'd need a name for yourself first. And even then... People like to see it in real life, before they shell out big bucks.