It wasn't until I had worked on transcribing some of Naudos stuff I it started to dawn on me the number of different skills needed to be able to do what he achieves. Probably the key skill is to be very well versed in music theory - be it learnt the hard way from schooling, or learnt "on the job", as you go, intuitively "music just makes sense" style. Seeing as I have very little schooled or intuitive music theory (being the programmable guitar playing robot I am), the other skills that I started noticing I had a shortfall in was bass, and rhythm.
You ever played a bass guitar? Picked it up, realised it is just the lower 4 strings from a 6 string guitar, figured "that's gotta be easy enough!" and then discovered you couldn't really do anything with it? Yeah. I've had a bass guitar for more than 10 years, I used it while I was writing original songs circa 2000. I bought it when I realise a detuned 6 string does not sound as good as a bass guitar. At the time my bass prowess was generally just 4 beats per bar of the root chord note. Not very exciting.
I think the first thing you need to accept is that playing the bass guitar is quite different to playing a "normal" guitar. Bass guitar players think differently, it's like they *feel* a beat. I've started to just touch the surface of what is going on in bass playing - because in fingerstyle, you need to have some bass skills. For example, playing the current root chord note 1/8th before the next chord note. Or, while in chord, go down a fifth then back up again for a groovy "bah-da-dah" 1/8th before the 3rd beat in a bar.
Check out some bass guitar players. Get some ideas! Fingerstyle basslines won't probably be as cool as a soloist bass line, there is only so much you can do while playing a melody as well, but there are plenty of tips to be gleaned.
The other skill I've developed a little bit on the side is drumming. Even just to learn and co-ordinate a basic rock beat can help your fingerstyle. Especially for those of us who don't have a natural rhythm. Not only are the drums good fun as well, but it is quick and easy as a beginner to get skills of basic drumming just from watching internet tutorials.
I reckon the skills you'd learn from lead guitaring are useful too, but I was never very good at lead guitar, nor did I enjoy it. If learnt lead guitar from a music theory point of view - knowing how to improvise over chord progressions and that sort of stuff - very useful, that takes me back to the key skill I identified during my Naudo transcriptions; music theory.
But, if like me you just want to get some better bass and rhythm into your arrangements, do some bass guitar and drums cross training!