Just brain storming here, but what would be the impact of allowing a luck burn modified roll of 20 to succeed? So instead of adding in your save bonus if the DC was super High you could burn luck to essential make the roll a natural 20 for save purposes and thereby succeed. It has lasting effect, characters would be hesitant to do it, and it incorporates a mechanic that is already in existence.
So, if I burn Luck to bump the total of whatever I've rolled up to a 20, that's a successful save, no matter what -- but it's got to be enough Luck to also cover my regular bonus to that save, to be an auto-save... hmm....
e.g., I have a +3 to my save and need to save vs. a 27 -- no possible way to roll that normally. So I roll, and get a 16 on the die, which takes me to 19 total. I could burn 8 Luck as things are to make the save. But your proposal is that I could burn 4 and it'd be a success...
I guess the issue I see in this is that, if the Wizard got to the 27 by his natural numbers (caster level and ability), if I can burn only 4 Luck to make it, it feels like I've nerfed his natural ability. If his roll was a 21, and he spellburned to get up to that 27, making the save the 21 (my suggestion) seems more appropriate -- it acknowledges his natural ability, allows him the benefit of the spellburn to get more oomph, but still makes the save something doable (perhaps with a cost to the target anyway, even if it's not the 'cost' of suffering the spell itself, it's still a cost in Luck burned).
Basically, burning-Luck-to-make-a-20 makes it so a Wizard could have a *very* successful casting, but maybe I only burn 1 Luck and -- Ha-Ha! (Nelson voice) -- I just avoided the smackdown.
Gnome Boy (a.k.a. "Jon") • DCC play-tester @ DDC 35, Feb 2011. • Beta DL 2111, 7:00 AM PT, 8 June 11.Playing RPGs since 1977
• Quasi-occasional member of the Legion of 8th-Level Fighters.
Link: Here Be DCC Monsters