I can understand you about the materials… it took me quite a lot of time and money to find the right materials, properties and techniques before I reached perfect castings. My company is making 99% engineering parts, most of them are complex and with tight tolerances.
There are a lot of great urethanes with properties very, very close to those of the thermoplastics infact. After trying a lot of brands, I can say we are now settled using Axson and BJB - I can hardly tell the difference between them and thermoplastics. We are using urethanes close to ABS, PP, Nylon, high temp, rubber and fire retardant, there are rigid urethanes which are fine with temperatures >150C. I am also making overmolding - steel inserts, pins, rubber, etc.
Of course it took me a lot of time to get perfect results - most of the magic is when you prepare the part for molding and especially creating the parting line and vents. This is not something I can describe in a few words, it just takes a lot of thinking, reading & practice.
Here are some parts that I have vacuum cast:
https://drive.google.com/drive/folders/0B3BqL-smlR6RbDl0VFMzMTN1RDQ?usp=sharing