Alter Selt, Disguise Self, and the Disguise Skill

I am currently playing a changeling bard in an Eberron campaign, and he specializes in disguising, bluffing, and diplomacy and such skills, though not really to the point of munchikinism. He recently levelled to level 4 and gained his level 2 bard spells. I chose alter self and glitterdust.

Alter Self, according to the spell listing, when used in making a disguise confers a "+10 bonus on your disguise check", disguise self - as per the spell - also confers that same +10 bonus. When I mentioned that using alter self when creating a disguise I could have my disguise check at +33 (then modifiers for race, sex, etc... would be added later). Instantly we had an argument. Alter self and disguise self are both spells, and one person said they confered 'magical' bonuses and thus did not stack. I maintained they would because the spells read "bonus" which stacks with other "bonuses". Another point also came up, could it be that alter self does not have the ability to control details, and just mainly shape while the disguise self would be able to control details on the new form, thus they would be able to stack. Yet other people argued they do the same thing anyway.

So, I said we'd talk about it later, and I'd ask here. What are your thoughts?

I can see two interpretations:

1. They don't stack, not because they are similar bonuses (they aren't), but because one effect makes the other irrelevant. From the SRD, "Sometimes, one spell can render a later spell irrelevant. Both spells are still active, but one has rendered the other useless in some fashion."

2. They stack. You apply the alter self form first (a transmutation) and then alter it slightly with disguise self (an illusion). Perfectly reasonable.

There was a rather large debate on this a few months back.

I'm on the side that, so long as you use them together appropriately, they stack.

Your Changeling ability to alter your form does not allow you to alter your garments. The Disguise Self spell does.

So, use your changeling ability to make yourself look like the person, and then Disguise Self to make yourself carry all the appropriate accoutrements (weapons, jewelry, signet rings, clothing, etc.). Then, should anyone see through the illusion from Disguise Self, they'll see the same person standing there, but with different equipment.