Hey i was wondering if it is worth buying an ibanez guitar with a locking tremolo if i already have a non locking guitar? and also can i change the tuning by only using the fine tuners?
Its worth it if you think it is, no one else can decide for you.
And with a floating trem, you need to set up the trem every time you change tunings, so its not really worth it, they're usually left in one tuning all the time.
It depends. I'd say that locking tremolos aren't necessary unless you want to do crazy whammy tricks. As for the second question, no, it's not possible to change the tuning with the fine-tuners only, because of the way a floating tremolo works. Altogether, changing the tuning or the strings is often quite a hassle, so if you're not prepared to go high-maintenance with the tremolo, don't do it.

Guitars: Ibanez SV5470F, Ibanez Xpt700, Fender MIM Standard Stratocaster ('04-'05), Jackson Ps-2
Ashton AG200,
Amps: ENGL E530, Bugera 6262-212,
FX: TC Electronics G-major 2, Behringer EQ700, Morley Volume / Wah
do you mean a strat style bridge by non locking guitar or a simple fixed bridge? you need a double locking trem if you wanna do crazy whammy stuffs. otherwise a strat style bridge is alright. and you cannot change tuning using fine tuners but only fix the tuning after locking the nut or after the tuning is dropped a little bit after heavy whammy use.
My Guitar Rig:

> '09 Ibanez RG1570 Mirage Blue w/ DiMarzio John Petrucci Set
> ESP LTD V-50 Black
> Line 6 POD X3 Live
> Dunlop DB-01 Crybaby From Hell
i agree with what litle phil said and by using the fine tuners you probably won`t get more than a 1/2 step in pitch anyway.