UMD doesn't seem viable on a cleric build to me. Trying to work it in myself right now. Even with a high charisma the UMD req on arcane spell scrolls/wands is really high.
http://ddowiki.com/page/Use_Magic_Device
Reasonable UMD to obtain
Max UMD from skills at 20 is 11.
Charisma mod. 14 base + 6 item + 2 ship + ap is a = +7 mod
Competence mod, golden cartouche +3
Enhancement bonus, big top +1
luck bonus, Voice +1
planar gird GH +4
alchemical bonus, eagles skill +3
Total of 30
You can stretch that some by getting some epic end game items, epic big top etc but still leaves you far from the better spells. And most importantly you have to neglect balance/jump completely.
/shrug, UMD looks much better for a non divine class because you can get easier/quicker access to healing items than you do the good arcane items. I may be wrong, but it looks like UMD on a divine is a skill you'll dump points in until level 20 and only at level 20 with a lot of farmed gear will you begin to get minimal use out of it.