Without a new 4 channel amplifier to go with it, not really. Aftermarket amps don't work with the rear OEM 6x9's so now you're replacing those as well. The JBL (HKs) are a nice entry level and coupled with their 6x9 counterpart (
GX963), with a mid-high quality amplifier, you will notice 4x the clarity at a reasonable price. There is simply no such thing as cheap audio upgrade, no different as asking for a cheap path to 500 RWHP, it doesn't exist. Spend the $1,000 and don't think twice about it.
The
Sony XM-GS4 recently won first place in a blind amp shootout review testing entry level amplifiers in a SQ peer group I'm in. Beating out the Alpine PDX-F4, Helix, JL audio and even Zapco ST series. None of this probably means much to you but basically, the Sony XM GS4 is the best money can by at this price level right now.
Equipment:
JBL GX600C; $80, Newegg
JBL GX963; $80, Newegg
Sony XM-GS4; $250, Crutchfield
Installation for above; $100 x 3
Miscellaneous:
Fark Harness; $130
RCAs; $50
AMP Kit: $60
Metra front speaker adaptor: $15
Metra rear speaker adaptors: $35
Best Buy may or may not change some of the miscellaneous charges or nickel and dime you $5 here and there, but don't pay more than $1,000 + tax out the door.