I hope not, because4 I've been recommending it to people. Glad to see you are joining the GT3 crowd, milefile.
Most people run the Speedway race in the Clubman Cup or Sunday Cup. That gets dull fast.
If your Miata is all bolt-ons (no lightweight, no port/polish) I recommend you take off all the speed parts, buy a set of T2 Super Slicks for 10,000 credits or so, and run the Roadster Enduro. This nets you 100,000 credits in about an hour, and a chance at some really good cars - even a 25% chance of getting an F1.
One thing - do you know about the virgin oil change trick? Change the oil on any car you buy or win, before you drive it at all. For a mere 250 credits, you get 5% additional horsepower over the base number.
Another thing - I know money will be tight, but I recommend against selling any of your prize cars unless they are totally redundant. You only get 25 cents on the dollar for them and you never know when you may want one later. Just change the oil on them and leave them.
Hope this helps.