When using the adventure points to improve my character, I was wondering how effective it is to spend the points leveling attributes.
It comes with such a high cost, I have been sticking to improving skills and spells. I also improve vitality directly.
I would be interested in what other players of this game have to say. Thanks.

Yes, you should increase attributes:
1) The upper limit to which you can increase your talents and spells is limited by the attributes - it's "highest related attribute + 3". So at higher levels, you will no longer able to improve your talents / spells until you level up their attributes.
2) Attributes increase things that you can't increase directly, like Stamina, Magic Resistance and weapon damage
3) What special attacks you can learn (those are very important) is often limited by attribute values

My advice is to save up some adventure points once in a while to increase one of your important attributes (depending on your class). Also, I would improve vitality directly for a few points, but after that it becomes too expensive.

yes well worth it. At lower levels don't worry about it unless you need to pick up a skill and your off by 1 for needing it, you won't get much aps early on and those are better getting your basic skills up.

But as you enter midgame +, you should start raising them some, you don't need to do it all the time, you'll have skills you need, special moves you need, but start raising attributes once in a while. warriors of course strength for more damage, tec. If your a skill heavy character raise up those lower skills so your success happens more.

But don't over do it. make sure your picking up all the special moves you'll be needing, make sure your weapons skills (or magic) is up to par with how far in the game you are. Some skills don't need to be super high mid game (pickpocket, etc), haggle, speech, etc. but some you might want up more (animal and plant lore, survival) or what ever.

But stats are just as important as the other 2 catagories of skills and special moves, so midgame start getting them up as you are out gaining more aps than earlier chapters.