If you go by recoomendations and certificates, I've found they are all mostly bullshit anyway. Many will say that having all lvl 5's in skills are a must for the certificate and that this and that certificate is then 'needed' for the ships and such. Utter rubbish. I've not seen the need, for instance, in gun spec 5 of any given gun. It takes forever and only gives a 2% damage increase per level, you only need level 1 to use the T2 gun anyway - take it to 4 and leave it at a respectable 8% increase in damage, why waste weeks, or months, on that 2% increase?
There are a multitude of other examples, like [racial] drone spec 5, fighters 5, the advanced learning skills on 5 etc.
On the other hand, basic support skilsl like hull upgrades, engineering, navigation, shield upgrades, mechanic, weapon upgrades etc. are not jsut good to have on lvl5, but quite needed for alot of things I take for granted these days. I can't tell you how frustrating it is to not be able to fit that mod your main has had available for years, on that nice industrial toon of your because that spesific skill was not lvl5 yet and so on...
Entire thing's about balancing it out, gettign the needed/useful skills to 5 and leaving the ones that are not too important on 4 and such.
Skills granting new abilities and ships to fly are part of my motivation too. I love the sense of real progress tihs game has. There is no end game. A god of PVP am I? Can still master so many industry skills, to name only one alternative.
That and RP. And the PVP. And to balance out PVP and to have another sense of progress and prowess, industry. I can't wait to sink my teeth into industry and T2 production and research. Self-built Toys, hell yeah.