I'll probably echo a lot of what has been said here but here are my 2c:
1 - Offensive casting isn't being used instead of healing, it is being used to avoid healing. You need to know how to target your spells though. Command is a will save spell, it does not work particularly good on casters but will usually work on all melee types (other than undead,constructs, ooze). Soundburst is a fort save, try to target it so it hits enemy casters primarily as they have bad fort saves and they also usually hurt the party the most.
2- You mentioned catcombs as being a pain. At low levels turn undead will be effective if you do a few things. Cast eagles splendor (or pot it), cast that level 2 spell that boosts your turning and wear a sacred item. This will be effective up to around level 8. After that it can still work but your burst from RS will probably be more effective.
3- Start each quest with a SP item equipped, it will likely be gone after buffing so you can switch it. At low levels mine was a rod that I switched to a shield.
3a EDIT - Buffing is important use the appropriate buffs for each quest and you will save thise buffs on healing. Dont feel the need to throw 6 of each type of individual buffs though unl;ess it is critical. You will waste your SP that way.
4- Use the highest devotion item you can. You have high level, alts use them to buy this.
5- Prioritize your heals - you know who the drains are and who are effective. Prioritize those effective ones. If you have 5 drains, wait for the wipe without using wands and drop.
Goodluck. Once you get to higher levels you will probably love your cleric but can be rough to start.