You're really asking about two different things, strings and the guitar body. Another area of hot topic is also the fretboard.
For a classical guitar, you generally have these made from two materials: nylon (or some other synthetic or semi-synthetic material) and steel windings. The life of these treble/bass strings are totally dependent on use. Your perspiration chemistry will determine how well these hold up to standard use and abuse. But in general many players use a dry microfiber cloth to wipe the strings off after use. This usually helps most people with sustaining the life of the average string. For those of us (myself including) with more damaging effects on strings; treated wipes or applications can be used too. It's important to remember that anything you put on the string shouldn't be put anywhere else on the guitar though; as the testing and "guarantee" of such item (if it even exists) will only apply to the strings themselves.
Like the strings mentioned above, bodies can consist of many different woods and even more finish types which all will have different reactions to solvents used for cleaning on them. In general; most players and manufacturers will agree that using rubbing alcohol on a finish like the body (or top, back, sides, neck, etc.) is a bit too harsh of a cleaner. Depending on the finish type; the alcohol could (worse case) eat away or wear down the finish, or even cause it to "cloud" over and haze. Most guitar owners clean their bodies with dry, lint-free cloths, and many manufacturers suggest this same method. Like Taylor, Alvarez (expand "How Should I Clean My Guitar"), and Martin. Some manufacturers recommend a polish (as in a few examples above) but note their suggestion of a clean, dry cloth for cleaning the body.
Fretboard (if you care)
You didn't mention the fretboard but I can assume that it may come up, especially if you happen to get some rubbing alcohol on the strings (and potentially the fretboard). Rubbing alcohol tends to have a drying property and the same can apply to untreated/finished wood, which generally is the most common type of fretboard on a classical guitar. It's important not to get anything on the fretboard as most manufacturers will not recommend it.
Continuous application of rubbing alcohol to an unfinished fretboard will more than likely cause it to visually look dried out, and even may cause the wood to crack inside the grain.
If you are going to use rubbing alcohol use the suggestion that most cleaners have on the back of bottles: use it in an inconspicuous place to see if there is any sort of reaction.
But best bet is to go with something specialized from the manufacturer, or just a dry lint-free cloth to wipe away smudges and grime (if it's really bad, dampen the cloth ever-so-slightly, but be sure the finish doesn't sit with water on it).