d20 3.5 System Reference Document states:
You confer on the subject the ability to see all things as they actually are. The subject sees through normal and magical darkness, notices secret doors hidden by magic, sees the exact locations of creatures or objects under blur or displacement effects, sees invisible creatures or objects normally, sees through illusions, and sees the true form of polymorphed, changed, or transmuted things. Further, the subject can focus its vision to see into the Ethereal Plane (but not into extradimensional spaces). The range of true seeing conferred is 120 feet.
True seeing, however, does not penetrate solid objects. It in no way confers X-ray vision or its equivalent. It does not negate concealment, including that caused by fog and the like. True seeing does not help the viewer see through mundane disguises, spot creatures who are simply hiding, or notice secret doors hidden by mundane means. In addition, the spell effects cannot be further enhanced with known magic, so one cannot use true seeing through a crystal ball or in conjunction with clairaudience/clairvoyance.
The primary reason I suggested this is because, for issues of game balance, Howland seems averse to a spot bonus, and since I do not believe there are any spells that bestow a search bonus upon the wielder, aside from Fox's Cunning, it would be a way to make it a more useful spell without damaging stealthing characters.
For a more logical reason, pertaining to the gameworld itself, the spell description explicitly states that it does not help spot hidden creatures. Hiding is not a pseudo-magical feat, and epic hiding, while essentially supernatural in nature, does not really apply on EfU, save for possibly some epic-level NPCs.
Now, the spell-description does say that it can help spot secret doors hidden by magic. I believe locating hidden doors is a search check, as is locating traps. While it is certainly true that not all doors in EfU are magical, and not all traps are, a search bonus is a better fit for an addition to the spell, because the spell does have a limited application in regards to search, whereas it explicitly states it has no regard to hiding creatures, which would be associated with spot.
For additional rational justification, consider the "see as they are." Hidden doors and traps rigged along the floor are far more likely to fall under this line than a creature simply hiding behind a wall, or some sort of cover, because as the spell description states, it does not confer X-ray vision. Hidden doors and traps are, by necessity, typically exposed at least in some fashion on the surface upon which they reside, which would allow for a True Seeing spell to, sensibly, be able to help boost search to a degree. Per the spell description, it does not help spot mundane hidden doors, but a search bonus would merely boost the user's ability to discern out-of-place things, and thus it seems a sensible means to add slightly more power to this spell.
In short, search does make more sense than spot, if you look at the spell description. You can try to make a weaker argument that it should grant a spot bonus as well, but again, Howland seems disinclined to allow it, so search seems a reasonable alternative.