In DE there is already a lesser Ars Magnus called Yuuse Batto Jutsu that allows you to make the samurai style sword drawing at lightning speed and a full technique tree (Meizo's Way). I totally agree with Void Cabbage in reguard to Batto Jutsu Module, anyway. I used a Weapon Master who hid inside the armor 5 couples of different weapons and being capable of switching them at will without penalties allowed me to play extremely flexible tactics which made fighting a lot of fun (despite fights being possibly the worst part of this game due to the extremely slow game mechanics).
As a general rule, most Style modules (and weapon modules) are extremely costly for non-weapon master characters, so I wouldn't reccomend most fighters to buy them, except perhaps for most useful ones (like the Defense Against Projectiles Module for characters wielding a two-handed weapon).
As for buying DPs, this can be a worthy expense at most for classes that spend 15DP per multiple (Warrior/Paladin/Dark Paladin). Although 15DP for 8HP might seem a bad expense, there aren't too many ways of increasing your HPs and spending CPs on increasing CON is always a good idea, regardless of class, but especially for "physical" classes, so the bonus HP will increase as soon as you get more CON and with a CON value of 15 you have a reasonable 1HP/DP ratio even for such classes. Of course, Weapon Master is pro in this, since Weapon Master is the absolute Tank class in Anima.
As a HUGE DP dump, I'd rather point out Wear Armor for ALL classes that spend 3DPs per point in it. Seriously, the character won't ever be capable of wearing anything decent...just stick to Armored Longcoats of increasing quality! Even for other non-Weapon Master classes I've got my doubts about the usefulness of spending huge DPs on Wear Armor ability...and since I only think that spending on Wear Armor is useful if you want to access GOOD plate armors, I can't see much use in spending at all on it unless you're a Weapon Master or at least a Paladin who gains +10 Wear Armor/Level (or unless you spent CPs on Use of Armor Advantage).
As for Supernatural or Psychic Abililities for non Magic/Psychic Class, there are only two cases in which i would advocate them. The first is when building a character obliged to take either The Gift or Access to Psychic Disciplines but going for a non mystic/psychic class. After all a Duk'Zarist can be a technician and a Sylvain can be a Ranger right? In all these cases I would strongly reccomend to invest non-Combat DPs on the other primary ability in order to make it at the very least usable. Projection Modules are always useful unless you count on using only Effect Spells and self-boosting Psychic Powers (essentially from Physical Increment Discipline). As for the rest..spend on permanent Psychic Points for psychics (to increase base Potential and buying FEW useful Powers) and MA for casters. As for Paths, I'd definitely avoid attack oriented stuff, since your primary way of attacking will still be dealing blows. Earth/Air/Creation/Essence/Illusion are all paths that work very well for granting utilities to a fighter as well as War/Blood/Nobility/Time Subpaths (also Darkness and Light may come in handy, depending on the chosen class). Same goes with Disciplines (and yes, it hurts a lot that Duk'Zarist are obliged to take Pyrokinesis as their first), where I'd reccomend Physical Increase, Hypersensitivity, Teleport or some Psychokinetic powers. Also Electromagnetism and Telepathy can have their uses actually. Note: Path or Discipline is completely useless, just there are some that will do better for a fighter class, especially since you're not investing too much into them. Anyway, the second reason for a fighter class to spend on Magic/Psychic is for a Warlock/Warrior Mentalist who changed class to a pure Fighter or a Fighter Prowler or Domine class (you usually do this if you want at some point your Warlock/Warrior Mentalist to use techniques or Ars Magna, which would cost too much on the multiclass character). Such change allows the Multiclass to concentrate on fighting after having reached a decent enough level on his Supernatural Abilities, still there is no reason not to keep investing on these even if the growth on them slows considerably.
As for the other DP dumps...Additional Attack Module: I never liked it too...making additional attacks in the traditional way is not that good, due to the huge Attack penalty, and adding more penalties isn't that great even if the opponent gains pealties for additional defenses. A character with Noah's Elan might though greatly reduce such penalties, but then again, even for a Weapon Master there are better places to invest the extra Combat DPs.
Block and Dodge?! Lol...
Ki Powers permanently decreasing stats...Never used them (and changed the final technique of Hypnos Requiem so it didn't have this disadvantage that made it trash), just like I never used the Final Technique Disadvantage. Even Previous Preparation is not worthy on my opinion...c'mon what's the use of a technique that you need 20 turns to prepare (and that's for a mere -10MK cost!). All this stuff can be nice for very focused NPCs who develop a single technique for a single purpose, but otherwise I can't see any use for this stuff.
My two cents, of course.