I'm curious how often you re-string and give your guitar a good tune-up? Back in December I replaced the pickup rings on mine and took the opportunity to oil the fretboard, polish the body, clean the frets, and re-setup. I haven't re-strung since. For no reason in particular I'm thinking it might be time for another good cleaning.
I play for fun only and practice just about every day for anywhere from 15 minutes to an hour. On weekends I might get in some longer practice sessions.
Just curious how often others take their guitar to the spa.
That's going to vary from person to person, where they live, how many 'hours' they play, whether they have more acidic sweaty hands, how aggressive they play, what strings they prefer etc etc etc. If you use Ernie Ball's Paradigm or D'Addario NYXL's for example, you may get more 'hours' worth of life out of strings so may not need to change so often - especially if you aren't gigging. Oiling the fretboard too much can be detrimental too - especially if you use excessive amounts. A full set-up is really only necessary if you have to do it - usually a quick check with your string gauge ruler or what ever tool you use can determine whether you need to do a 'set-up' but more often than not, its unnecessary.
I tend to use a micro-fibre cloth and wipe the body as and when required, I keep my Guitars in their cases for the majority of the time and maybe have 1 out on a Stand so the don't really gather 'dust'. I don't gig either so I am not jumping about, getting all hot and sweaty and then packing up my guitar with 'sweat' on it as I have to pack up and clear out of a venue pretty quickly. Therefore my guitar isn't left with sweat on it for 'hours' which is also corrosive and shortens the life of Strings. Therefore a set of strings can last me more hours than someone else. I am also not subjecting my guitars to drastic environmental changes - taking them out from say a 'room' temp into a 'cold' environment and back into 'warm/hot' environments because they don't leave my house so they remain very stable - any 'temp' changes happen gradually and naturally. Therefore I don't need to do as much TLC, string changes, oiling etc as others may need to do.
It can be 'difficult' to notice the deterioration in strings as it can be very gradual - like you don't notice your hair growing for example - and they can seem to sound the same as you remembered them on day 1. Its not until you change them that you realise how much they have dropped off because the new strings sound brighter, more alive. The best thing to do is to do a string change - assuming you use the same brand and type of strings - and see if you can hear a difference. If they sound a LOT different, then you need to change your strings more often, if they are very close but still different enough, then you are at about the right time - unless 'gigging or recording' where you maybe don't want any noticeable 'difference'. It will be more trial and error as you find the right time for you. As for oiling and set-up, again that will come down to you and the hours of use, the environment etc. It never hurts to do a quick check, string heights, floating bridge height (if you have one), fret heights, intonation etc - all simple checks and if they are all consistent - even after a string change, then you don't need to do a set-up. it never hurts to wipe down the guitar with a micro-fibre cloth - especially if you leave it out - to remove any dust etc that builds up under the strings and give it a very light oiling of the fretboard - maybe not every string change but will depend on you and your situation.
There is NO hard and fast rule that everyone should adhere too as there are many different variables that can determine when its the right time for all of these. The set of variables are different for anyone so its 'best' to find out what works best for you and your situation which could be VERY different from me an my situation. You maybe won't know if its the right time to change strings until you have changed the strings several times to be able to gauge how much they have dropped off (if at all). If you play the guitar, then change strings and play the guitar again, and you can't hear a difference, then you can try going a bit longer next time but if you hear a bog difference, then you know you need to change them more often. After a few changes, you will know what's the right time for you...