My opinion.... if you have been running Mimaki's this long then stay with them. Everything will be immediately familiar and if you are still running ancient JV3 machines and go to the newest you will skip an entire generation (JV33) and the differences in how much easier these are to maintain now will be just about stunning to you. Even the JV33 machines are far easier to deal with than the JV3.
Latex does have its place and has improved a LOT but it will still be a big change from what you are used to. Also don't buy into the "iphone" of wide format and "ecologically friendly stuff. Yes they are the trendy thing to have and all but if the HP needs dual 240V 16A circuits (they are pulling 4600 watts when printing) versus the Mimaki's which use far less power only needing a regular 120v plug outlet. The JV150 (most comparable step from your JV3) only pulls a max of 1440 watts, even the dual head JV300 (which would be a more direct competitor for an HP 360 speedwise) still only doubles that at 2880 watts and still used regular 120v plug outlets. Also like many so called"green" products, often times what a manufacturer has to do to make the product green by far offsets the fact that the end product is green. I really have no idea what goes into HP Latex inks so that might not be fair though. Regardless, if the printer is using double the energy to produce the same product than I don't personally think its really any "greener". Its about $$$$ and green is a hot buzzword that people will pay extra for – same with recycling, by far recycling is much more about profit than actually helping the environment. The inks themselves - again, not really sure. I do know the VOC's in the HP latex inks are below gov't thresholds for being an issue. Of course there is the very big advantage of the HP latex in that the prints are "usually" immediately dry after the printer cooks... er.. I mean cures them. Another plus - the new JV150 and JV300 machines, if you want an extreme color gamut, well with their new orange ink you would flat our blow the HP's color gamut away, not just beat it.
Please don't get me wrong. I'm not totally knocking the HP. I think in the long run there will almost certainly be a move away from solvent. Currently though, solvent is far from dead and pretty much all wide format printer manufacturers are still designing and making brand new solvent model printers. The HP has some nice things sure like a built in like the i1 spectro for creating color profiles and prints that are immediately dry are of course an obvious big plus. I just see many people on the web going "apple fan" blindly fanatical about them without giving any realistic hard evidence or independent proof to some of the claims being made. Its also amusing to me that for a very long time Grimco was a big Mimaki dealer too. Just like most things its all about the money and we are all going to push what makes us the most money, even if it means to an extent steering a customer to the item we represent while not really educating them on the real differences between competing products.
In the end Gino had it very right. You need to get what is best for you, not necessarily what every else says is the best.