Hi Gav,
Welcome to the TFP Forum.
I think whether you need Envisioneer or TFP probably depends on what you want to use the program for. TFP replaces FP3D in its ability to create a building in 3D, walk around it and generate photorealistic images. Its walkaround abilities, flexibility, and rendering speed leave FP3D for dead and I have not used FP3D once since I switched to TFP as it does nearly everthing much better. Like FP3D it does not do a great deal with plans, as far as being able to use them to submit to councils - Envisioneer does that. Whether that is worth another $1300 (I thought it was about half that) depends on whether you are a builder or not and whether you can aford to use other programs to make those plans, such as TurboCAD or AutoCAD (BIG BUCKS!).
The term PRO is not a comparison with Envisioneer (CADsoft product) but with TFP Home and Interiors and TFP Landscape and Deck, (IMSI products). Theoretically we do not know that it is related to Envisioneer, as that is programmed and sold by CADsoft while TFP is owned and sold by IMSI, so in that sense the two cannot be compared. It is also related to 3D Architect and maybe others too. True they do use some of the same elements, probably most, and the names underneath may say Envisioneer in some cases but this is the same with many things today - just look at cars and appliances!!
To be honest, even though I used FP3D for longer than I care to remember (from v3), I cannot recall now how the import worked. I certainly do not have any problem with TFP in that regard. There are so many ways to do it, as there are with almost everthing. Probably just a case of what you get used to.
What does the patch do? It certainly does not add blocks, but fixes a few things, mainly to do with rendering (render as a JPG now works, a cloudy and overcast option were added to help balance interior and exterior lighting and a problem was fixed that caused TFP to crash for some when doing Advanced (Radiosity) rendering. If you do photrealistic renderings, then the patch is significant. If you don't, then it may not be worth the effort.
Allan