Retaining “hit dice” makes sense, since this doesn’t tie level (challenge rating) directly to offensive and defensive power and precludes mage-types (low offensive/defensive, high special power). In this case we can surmise that at least in the case of devils, all saves are 10 + half HD + relevant ability score modifier.

Touch AC according to your source seems to be AC -4. I don’t know if this is a general thing or it’s derived some other way. I’m going to go out on a limb and assume the former; it makes sense.

With seven hit dice, it’s entirely feasible that the creature received 6HP per level (42HP) plus a flat 5 for Con modifier (total 47). But does the 6HP come from 1HP/HD and 5HP/HD Con modifier with a bonus Con modifier at first level, or is Con modifier applied only once per creature?

Point Blank Shot… This might explain the disparity between melee and ranged attack. Are we seeing +2 attack from hit dice, +7 from Strength on the melee and +5 Dex / +2 from Point Blank Shot (and optionally Precise Shot)? No, I don’t believe a 7HD creature would receive only one third hit dice in base attack. Or would it? If the one-third theory is true, an ability score of 10 offers the average person +3 base.

Damage, I still can’t work out why the claws deal +4 (half modifier plus one?) and the spine rain deals +2 (from Point Blank Shot, perhaps?)

I interpret the nethersight line rather differently: my quess nethersight is a particular ability (the ability to see into the nether regions between planes?) that grants +5 to perception, the other 5 comes from Wis. This suggests that skills have no base – no HD.

The absence of a listen check suggests to me that listen is dropped altogether, spot covering the whole “notice something” role.

As to poison, I believe there is either no roll to save vs. the poison – if you are injured then you are poisoned, or the spined devil would roll (again) against your Fort to see if you are poisoned (and slowed) possibly for 5 rounds.

All good fun this guessing stuff isn’t it :)