I dont see how every cipher can be cracked. I can see this one being cracked if I encrypted a large amount of text. (Even though I took measures to stop that)
Also %_ is just two symbols, i eliminated spaces in the cipher text.
Well... it was worth a shot. Your right, the more characters you have, the easier it makes the job of analysing the string - especially using frequency analysis as it increases the data (for calculating IoC [index of coincidence]). Eliminating spaces and characters marking the end/start of words is your best bet.