I think a compressor to even out highs and lows when fingerpicking. Reverb to fatten up the sound, and if your guitar doesn't have one onboard, an equalizer. Don't be that doofus at the local bar playing "brown eyed girl" with 20 effects maxed out. When using effects with acoustic, the listener should almost not be able to tell you're using any. Unless you're that guy from CAKE who uses distortion with a classical guitar, and does it proudly.
I strongly agree with this...if you want lots of effects and sounds then simply play an electric guitar with all the Gee Whiz stuff. For and acoustic/electric you can "fatten up" and "enrich" the sound with Reverb, Chorus, and Delay...but fight the temptation to overuse the effects. The compressor (as mentioned) can even out the highs and lows.
Middleaged Redneck sorta guy who refuses to grow up...passion for music, especially Southern Rock but like bout everything cept Gangsta/Hip Hop. Collect guitars, mandolins, and love to ride Harleys.