I think the problems with these are more the exceptions(creature abilities never meant to belong on PCs, disproportionate ability scores, absurd natural attacks), without which polymorph-like stuff isn't that bad. For teleportation, its accessibility, and preventability(I've seen the potential for telefragging with rain, leaves and other floating shrapnel). Being able to go to places you've never seen personally can be an issue.
So my say of what to do with them is:
Transformations - Specific lists of form archetype stats modifiers, grant typed stat modifiers instead of wholesale replacing ability scores(and thus rendering said scores irrelevant). So you got Small Quadruped, Medium Quadruped, Large Quadruped, Small Flier, Medium Flier, Large Flier etc.
Also, grant only abilities and senses from a specific list provided with the spell(expanding said list for higher level spells), ensuring that said abilities are in line with spells of the level.
More narrow spells can bypass the above factors. Full stat replacement spells with SPECIFIC creatures, etc.
Teleportation - Lose the off target chance. Go with more specific and how far off target you can get. Better teleport interdiction without magic(rain, falling leaves, etc causing teleport mishaps).
For example.
Condition | Min Off targetness(weaker spells may be offtarget more)
'Live' sensory feed | Perfectly accurate
via scry, eyes or |
familiar |
Recent image, exact | 10xrandom factor feet off in direction
relative position |
or intimately familiar|
i.e. lived there |
Visited before or good| 100xrandom factor feet off
description |
Vague directions or | miles x random factor off
very outdated image |
Vague description | Good luck
EDIT: For horizontal displacement of course, vertical would send you into rock nearly all the time unless you aim for midair appearances and feather fall the rest.
