Ok, here is the no joke deal. I have been a Makerbot user since an early cupcake, upgraded to the first released version of the T-O-M, bult several other bots inlcuding an Ultimaker. The original T-O-M had problems such as using the original cupcake motors, the failing MK5 DC motors, the heater resistors, so I had to pay my way through the upgrades. I never bought a Replicator1 mainly because of price, but also because I have tons of 3mm filament and never felt 1.75mm filament gave a tangible advantage.
Recently, I jumped back into printing and trying all the latest upgrades and came up with a few huge ones of my own.
Step 1 is you must use Sailfish firmware http://www.thingiverse.com/thing:32084
Just use the latest replicator-g version 4, choose the correct sailffish accelerated driver, use SF 50 and the T-O-M profile.
Next, modify your MK6 extruder simply by cutting 2 slots or holes in the thermal barrier tube and adding a 40mm fan to actively cool the tube. http://www.thingiverse.com/thing:34616
Notice the fan's placement so that it blows slighty underneath the metal thermal plate too. This is critical.
By doing those 2 basic things, your MK6 will be as good as, if not better than any MK7. I know , I've done the double blind test. Sailfish default settings are nearly perfect. I garantee, if you make those mods, you will be impressed and it cost next to nothing on hardware you already own. Sailfish adds so many features and improvements I cannot even begin to praise it enough. This is what you should have had from day one.
Next, if bigger build size is your desire, I already proven the gen4 electronics and MK6 can be optimized to be nearly perfect, then just take thsoe and put them in a bigger, better stronger frame that can use bigger motors. In practice. I am able to upgrade a T-O-M to my new bot for around $200. http://www.thingiverse.com/thing:35372
Hands down, this beats spending $1800-$2200 on a new machine , that may not be as good in all respects.
Again, I want to be clear, you really must try Sailfish firmware as it is a night and day experience. The second tip to mod a MK6 makes it print as good as any MK7/MK8 I have seen, even in PLA, somehting that previously didn't work that well. If you check out the makerbot operators google group, you'll see a lot of guys with both Rep1s and Rep2 with some minor issues. Rep1 failures include HPB connector failures, Z platform sag, extruder and pinch wheel problems. There are mods to fix these but why should you spend money a new bot you have to fix? Replicator bypassed some of those problems by not inlcuding a heated bed, but caused new issues since it's a PLA only machine. Apparently, MK8 is not as good at cooling the filament path as my MK6 mod, and thus, the PLA jams on long several hours prints. To that end, I can now call my mod proven as I just printed for 96 hours on a huge print for the local high school. Not one single failure ever. Also, the amazing pause a Z height function allowed mutliple filament color changes with amazing perfection. Hands down, the firmware makes the machine, but the mod is the icing on the cake. I cannot in good fail, recommend to buy a new printer, over upgrading the hardware you already own for pennies, compared to the cost of a new bot.