#1
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?
#2
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.
#3
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.
Gear:

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
#4
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
#5
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.