As for encoding of data that the game uses in preferences (and not only), dump with meaningful names also significantly simplifies research, revealing most of information that needs to be known.
First step for decoding, that is specific to data in shared preferences, is mentioned in first post of the topic - URL decoding. Then, after base64 decoding, the data needs to be decrypted with Triple DES in ECB mode with 128-bit key "8a76f557475b615a6dcaedeaadd4d27b" (bytes of the key in hex). The result is also base64 encoded, so it needs to be decoded and the last step is to decompress the data as gzip. Below is a CyberChef recipe that implements the decoding:
https://gchq.github.io/CyberChef/#recipe=From_Base64('A-Za-z0-9%2B/%3D',false,true)Triple_DES_Decrypt({'option':'Hex','string':'8a76f557475b615a6dcaedeaadd4d27b'},{'option':'Hex','string':''},'ECB','Raw','Raw')From_Base64('A-Za-z0-9%2B/%3D',false,true)Gunzip()
And to illustrate it with examples, value for level 5 from topic's first post after decoding is:
{"CheckSum":"1EBXq7XeVC5e6TxnIVs/T9kE2J8rLG9IeYdOBc3Nxs9INiuzkhi6urMRRl858UeQdgjO1dLqpfw=","Offset":620,"Value":625}
and value for level 6 after decoding is:
{"CheckSum":"1EBXq7XeVC5e6TxnIVs/T9kE2J8rLG9IOjAKjtrE26cgX17n25az4rF8y2+JN4AVv8YyOpD9PI8AmbJGj0p2sw==","Offset":-836,"Value":-830}
both of which are JSON serializations of structures of "SafeInt" type that the game uses for values that it needs to protect.