Does adding more characters to the Enigma rotors improve crypto strength?
Does adding more characters to the (Enigma) rotors improve crypto strength?


Not really… since the weaknesses of Enigma go well beyond the count of chars per wheel! 

Of course you could – theoretically – think of using very big (read: huge) wheels with an insane char range. But, when looking at the “time” and “resources” you would need to invest each time you’ld merely wanted to encrypt and decrypt things with such a beast, it simply wouldn’t make much sense. Modern ciphers already blow Enigma out of the water in terms of speed, cryptographic-strength, etc.

Differently stated: the gain you would achieve by adding chars won’t be big enough to level-up good old Enigma into the realms of more recent and better preforming algos (like aes, chacha, et al). 

Also, as CodesInChaos already hinted in his comment, it would put you on a very slippery road with a good chance that you’ll end up introducing additional attack vectors. In a worst case, you could break one of the stronger parts of Enigma while ignoring the real cryptographic weaknesses that already come with Enigma; which would result in something like a (let’s just call it) cryptographic nightmare.

Yet, don’t get me wrong: for something like a non-public “student project” with the goal to have a truckload of chances to shape your cryptanalytic abilities… this could be fun to fiddle with and maybe worth thinking about for a minute. But if you do, you better be prepared to notice you’ll need to fix a whole truckload of nasty little issues related to Enigma. Simply increasing the char count will not do it.