The reason for Shvara´s sp cost is probably because it has more conditionals that other removals. You first need to field him (him being level 4 it is a decent investment noting that commonly he will do nothing outside of his close skill due to his low agi and hp and locks it´s user from playing an additional unit next turn). Also when his close skill triggers it hits randomly, thus if it doesn´t hit a proper target you will not get the removal effect triggered, or it may instead hit an opponents level 1 with the removal effect. Simelarly when the opponents hp is high enough on both targets hit, it´s only 2x30 damage for 1 sp and a level 4 not doing anyhing else (other than taking 40 hp worth of damage) that turn. To help him hit the effect against higher hp units the opponent will usually have some grimoires, other units or ss to help him, but this usually also costs additional resources making the effect have an higher effective cost than 1 sp (and still doesn´t prevent the random hitting or an opponent dodging it by not reviving his only unit the turn before (commonly done in thee case of bigger units like with big red)). Finally the cost is effectively 2 sp as you´ll either revive or lose an LP. All in all the sp cost seems fair though like most cards how powerful he is will depend on what you´re using against him.
As for overdose on MD augment, it costs 1 sp, 2 cards (one of which was a fielded unit therefore decreasing your own field precence a little aswell) and a set fase and does a decent ammount of random damage that turn. I´m not sure why the overdose MD augment combo would need to get nerfed, could you explain in more detail what you think is too good about it.
"Truly, if there is evil in this world, it lies within the heart of mankind.'