There are a few issues I have here. The first is that you can't compare favour items once their "equivalent" stock item is in the 3000+ range. This is because the favour item appears immediately, while items like Journeyman's Treads appears very late, almost in the artifact-level cost range. That's a huge duration in the game when the favour item was granting benefit but the more costly item was not.
Secondly, you have to remember that you cannot stack two of the same items. This means favour items give you stacking that wouldn't normally be possible. You cannot say that blood of the fallen is equal to two banded armours, because you cannot ever have two banded armours. In fact, if you want to upgrade your health above what one banded armour offers, you have to throw out at least 1500 for a Nimoth's or 1750 for a Hauberk of Life.
The cheap early game items offer the best bang for your buck, but you have to remember that you're only allowed one of each, so if you want more than the scraps of stat they offer (even if it is at a very reasonable price) you have to stack more expensive items. This is the real benefit of some of those favour items, particularly blood of the fallen, giving you a way to stack early on that would not normally be available.
I'd also disagree with your statement on symbol of purity. It is a hand-tailored counted to the UB's spit. There is no trinket in the game that has the same effect as it, and therefor it is quite invaluable. There are times I'd gladly part with upwards of 3000 gold for its effect. To say it's useless sometimes may be true, but it does not take away from the fact that in its ideal situation it's extraordinarily powerful.
1) it's not appropriate to compare favour items to more expensive item's like journeyman's or HoL. These higher end items are not accessible in the early game, and this is the part of the game where favour items are most significant.
2) when there is no equivalent item (as with symbol of purity) it is not appropriate to give a gold cost, since situationally the item may be invaluable since it has no equivalent.
3) you cannot compare stats directly in many cases because the favour item offers "stacking" possibilities that would not otherwise be viable, and certainly not possible at the low costs of some of the basic items like banded mail.