I just don't think you're going to be in the same damage dealing league as less narrow builds, especially if your only source of damage is spiked armor. If you're going to swim with powergaming sharks, don't build a one trick pony whose trick isn't that good.
But it certainly sounds fun.
Take a level of sorcerer for Enlarge Person and something else... maybe Shield. A large grappler can be ferocious, especially at lower levels.
Our group is usually a bunch of straightforward strategic builds but theres one dude who always plays a whip-and-net bard or barbarian with the weirder rage powers or other builds that are really flavorful and useful in specific situations. It's fun. The rest of us keep the power level high and his characters certainly generate more fun stories.
I've got a concept for a character in mind (basically ripping off Thibbledorf Pwent, whom you may know of from Forgotten Realms books)
Not a battlerager. THE Battlerager!!!!!!
umm... great concept,
but what exactly where you smoking when you thought Grappling is a good way to get high DPR?
as far as I can tell, Grappling has heavy action economy costs, which you can reduce via Feats, though it still precludes Full Attacks, and the only damage sources of it are equal to Unarmed Strike/ Armor Spikes... Except that you can't Crit with a Grapple Check (if you follow SKR's advice re: the intent of Crits and Combat Maneuvers), and you can't make 'special' attacks that you otherwise could with UAS/Armor Spikes.
Now, Grappling MAY be a good strategy to deal with/neutralize 'high DPR' opponents, but that is very far from actually achieving high DPR yourself.
There are other ways to optimize DPR that may be compatable with Grappling, namely Come and Get Me (once you qualify for it at 12th level Barbarian), but you won't be doing any MORE damage than any other CaGM build, and likely LESS (than any build who uses more effective weapons than UAS/ArmorSpikes). Grappling can be a useful tool in a martial character's tool-chest, and Barbarians are probably one of the best at it, but if you are expecting it to enhance your DPR in any way, you are just bound for disappointment.
EDIT: probably the only way to combine DPR and Grappling is by getting the Grab ability and multiple attacks, e.g. thru Wildshape or something. That probably won't be the HIGHEST DPR unless you can get alot of attacks though.
the tetori monk archetype is a good option for grapplng + being effective/doing damage,
but it obviously isn't compatible with the spiked armor part,
and it probably isn't actually going to win any DPR contests either.
but maybe you are OK with giving up the abilities you would if you use armor with it...
maybe your GM would let you substitute maneuvers for NORMAL attacks, e.g. normal full attack, not just Flurry (which can only be done in no armor).
if you can get natural attacks, e.g. claws or bite, you can use the druid/ranger spell Lockjaw to get Grab, which lets you combo Grapple+FulL Attack/Damage. Barbs and Rangers, as well as Half-Orcs all have ways to gain NatAttacks, and other PC-appropriate races can just come with NatAttacks.