What do you consider expensive? I can get just about any D'Addorio strings in a single set for about $7 (American) at the local shop. $7 doesn't sound too expensive for a risk on whether the strings will make your guitar sound better to me, but I can see how it would to someone else.
Consider string material, what you want your guitar to sound like (brash or mellow, loud or not so loud, etc.), and what you can afford to spend. How you want your guitar to sound will make a difference of whether to buy nickle wound strings, bronze phosphur, silk & steel, etc.
However, to answer your initial question, new strings will almost certainly make your guitar sound DIFFERENT. Whether or not the difference is a HELP is entirely a matter of your personal taste. Strings don't last forever, so if they're getting old just about anything will be an improvement in the guitar's sound. Putting lighter strings on may put less stress on the neck and allow a lower action, but then again maybe not. Depends on how your guitar is built.
- Zurf
Granted B chord amnesty by King of the Mutants (Long live the king).
If it comes from the heart and you add a few beers... it'll be awesome! - Mekidsmom
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