I would agree that there is not one answer to your question. I bought the exact Incra Combo you are considering about 1 1/2 years ago. I added the Master Lift and a Porter Cable motor along with the under table dust collection attachment. Before that I used a Rockler table/insert with a 35 year old Makita router and a version of the Incra positioner made specifically for Rockler for their tables.
I have found that my new Incra setup is extremely accurate; both horizontally because of the positioner and vertically because of the Master Lift. Everything I do on it turns out exactly as I want it to (unless I make a stupid mistake). I haven't found anything that the table can't handle accurately with quick setup and usually only with 1 test pass.
As for dovetails . . . Half blind dovetails are quick, easy, and extremely accurate. I made drawers that fit together perfectly after one practice run viewing the Incra video and instructions. Through dovetails are a little bit more difficult and required a bit more practice for me. They aren't quite as straightforward, but still are very accurate once you get the hang of it. Box joints can be a challenge since the accuracy of the joint depends, to some degree, on the tolerance to which the straight bit you're using is ground. If it is even a thousandth under the stated diameter, the joints can be slightly loose. If more than that, it can be a problem which can't be resolved because the Incra box joint depends on the diameter of the bit to get a tight fit. If you do a lot of box joints either find a different method or plan on buying the Incra IBox jig which permits you to adjust the cuts till they fit perfectly regardless of the tolerance of the bit. (This jig also works with a table saw which seems to be the preferred method for most people to cut box joints.)
I love the whole setup and wish I have bought it years before I did. However, if space is a real problem it might not be the right setup for you. All my tools, including the Incra table, are on wheels so I move things out of the way and the tool I'm using becomes the one in the center, so space isn't quite as big a deal for me. If you already have a dovetail jig that you are satisfied with and is easy to setup and use with dust collection, there are other router tables/fences/lifts on the market which are also accurate and easy to use. You can always make your table or buy a table and install either homemade or other accessories.
For me, the Incra was worth every penny because of its accuracy, ease of use, and the dust collection under table. Check on possible discounts from Incra. When I bought, there was a 10% discount on your first purchase from incrmentaltools.com (the retail site for Incra) on everything bought in the purchase. It's not a huge amount but it helps on the cost. One other thing, the shipping charges on this site are high, I think, but they package everything well and don't seem to have any damage problems.
Phone and online support are fantastic. I have never waited more that one day for a return phone call or email if I couldn't get them on the phone immediately. They answer every question very precisely and honestly.
Just so you know, I don't make furniture for a living; just because I like to do it. I still think it was worth it for me.
Hope this helps.
