To the OP--what do you mean by "racing"? It means different things to different people. Some people just want to push their car hard, and autoXing is good for that. Low risk, low expense, low impact.
Some people want to get out to the Big Track and drive the car hard. DE is a great way to do that. Risks are moderate, expense is significantly more than autoX, potentially high impact.
Some people need that wheel-to-wheel rush--"I am getting to that corner first!" Some form of club racing is usually the answer there, but the risks are higher and the expenses are greater than DE.
Spec Miata is a great way to go if you are in the "right" areas. In some parts of the country, the SM drivers seem to feel that because they
can afford to throw their cars away every weekend, that means they
must. This has led to the nicknames "Spec Pinata" and "Wreck Me Outta". Happily, it's not the case everywhere. Oh, and of course, you have to live with the stigmata of driving a "hairdresser's race car".
--DD