/3/ - 3DCG

Hi guys, recently I've been doing some casual 3D modelling, for various things, work, home, fun, whatever.

At the moment I'm trying to convert some models from games into 3D files, I just wanted to run my method by people and see if I'm doing things correctly.
So all of these files are in odd formats, usually I'm able to get an .obj or .stl out at the end, but these are generally low poly models which are missing lots of detail (which are textured in). At the moment I am opening these files in Inventor, and drawing up corresponding sketches, essentially just tracing these objects, forming the proper solids and then modelling my own changes. I do this because many of the models are always incomplete and I can easily make changes, and also because I can then produce much higher quality models which can split and actually made into functional parts that can be assembled. My concern is there might be a quicker way to do it, since I always have some simple 3d file as a starting point (presumably turning a mesh into a set of sketches is absurd) or that there is a better way, since a lot of the time I feel like I'm eyeballing things so they line up with the mesh I have. Software recommendations would also be appreciated for this sort of stuff.