You may get quite a few opinions on this one (if you do a "search", you will see a fair amount of discussion on it).
For a street car, the first thing I'd do is flush and refill the shock oil. If you notice an improvement and there are no leaks, I'd say you're good to go.
You can use the lever shock oil from Moss or motorcycle fork oil. Some folks also seem to use 20W motor oil.
If the shocks seem "shot", you need to compare the cost of the tube-shock kit versus using good, rebuilt lever shocks.
On a personal basis, I am using tube shocks on my racer (all four wheels). They are much better at resisting heat and fade in my experience (especially the gas units). And they tend to allow the use of softer springs. I created my own "kit" to do the rears. I do not care for the Moss kit: it is heavy and puts the shock at a funny angle. Mostly, one just has to flip the lower leaf-spring clamping plate and drill an upper mounting hole. I used the same Monroe gas shocks front and rear (under $25 each, locally). There are probably very few club-racing Spridgets that use lever shocks....I haven't seen any in recent years. I have not documented the rear-shock conversion, but my front tube-shock conversion is
~HERE~. . I also ran these tube shocks on the car when it was a street/autocross car and I was quite happy with them.
On my brother's Midget, which is more of a street-cruiser, I suggested he simply drain/refill the levers: they are fine for normal street use.
I am also building a "Spridget Special" and I will retain the lever shocks on that.
One of the fellows here at BCF rebuilds lever shocks and he has an excellent reputation....he may chime in.