Depends on what music you are listening. If it's todays overcompressed mainstream Pop / Rock / HipHop studio recordings then there isn't much point into investing much money into headphones. Musical structures are simple and the overcompression in the studio killed already all hidden details before the record company pressed the CD. It's just loud with a lot of bass. Every LoFi headphone can reproduce that. LoFi headphones would even have one good point over MidFi headphones: They hide the compression artefacts better that appear when you squeeze your music to 128 kbps MP3.
If you are into classical, folk, jazz, country, world music, live recordings, indie Pop / Rock / Metal , mainstream up to the mid 90's, electronical music, noise, ... then it is definitely worth to invest money into good headphones. There is hidden detail which you won't hear with speakers or with cheap headphones. You can dive into such music and discover new things nearly every time when you listen to it if you use good equipment and didn't cripple your music with too high compression.
So take a look at your music collection: Is it just modern Top Ten chart music, then you can't do any better. Keep your actual headphones and forget about HeadFi, as you would just waste money without gaining anything.
If your music is other than actual chart stuff, then dump those pesky 128 kbps rips first and rerip them to at least 192 kbps with an actual version of Lame (3.98), use a better compression algorithm (AAC or Ogg Vorbis) or even better rip them to lossless (FLAC, Apple Lossless, WavPack). After that think about mid or good quality headphones. Your wallet won't be happy, but you might walk around with a happy smile because you hear the hidden things in your music that most others will never be able reveal.
