Since you did not give us the trust provisions, I will guess.
Q: Does the executor have a responsibility to invest funds for maximum gain or is just putting in a 1-2% interest bearing CD sufficient?
A: It depends on how strict the trust instrument is. The trustee will incur liability if the investments are too speculative, so generally they invest very conservatively.
Q: Home worth 310K, cash in CD 60K. Could executor, not that they will, decide to hand the trust over to me?
A: Probably not, since you said this was a spendthrift trust. There may be provisions, however, when you get to be so old, that the trustee could turn everything over to you.
Q: Is it at their whim to hand over funds, whole or in part though it is my money?
A: It is not a whim; they must follow what the trust agreement says to the letter.
Q: For instance, is it up to them do decide whether I am to purchase a new auto or not?
A: Consult the trust agreement. Usually buying automobiles is pretty suspect since they are not investments but expensive assets to buy. In other words, it depletes the corpus of the trust.
Q: I am 50 years old and finding the trust very restrictive.
A: That is not the fault of the trustee; it is the wishes of the person(s) who set up the trust.