It's even better than it might seem at first glance. The damage bonus (Spikes references Brambles) is unnamed, so it stacks with enhancement bonuses.
Spikes is especially nifty when cast on a Maul (Complete Warrior):
Maul 15gp --------d8 (s)--------d10 (m)---------x3 Crit--------20lbs------Type Bludgeon
1d10 (20/x3) is okay for a two-handed martial weapon, but it's especially with Spikes, with +2 enhancement bonus to attack rolls, up to +10 unnamed damage bonus, (19-20/x3) crit. And if you blow an Exotic Weapon Proficiency on it, you can use the huge thing one-handed.
This is the same damage as a greatclub (PH), but the crit is better.
On the other hand, since a greatclub is a larger version of a club (per PH description), you might be able to use a Shillelagh spell (normally limited to club and quarterstaff) on a nonmagical greatclub, increasing its damage to 3d8. Depending on your DM, you might be able to then add Greater Magic Weapon and Spikes spell for some really nifty damage.
But your DM may decide that once a club has been affected by a Greater Magic Weapon spell, it's no longer a valid target for a Shillelagh spell, so you lose the damage die increase.
Check out how all four spells are worded (Shillelagh, Greater Magic Weapon, Brambles and Spikes), and check out the PH description of the greatclub, then ask your DM.