I suggest an experimental approach to answering this question.
Hi Ms. Playmate,
If you want to be viewed by men other than your husband as a MILF ("mother I'd like to fuck"), my guess is, more men will look at you and decide on the spot you are sexually desirable and they would like to fuck you if your breasts are larger. I can't express an opinion, though, as to whether a C or D-cup would be "large enough" to make a significant difference.
I suggest you balance this against the "fact" that a woman's perceived sexual desirability is not primarily a function of her breast size. Rather, it's a function of her body-language signals (indicating she wants to fuck [or not]), her verbal facility (is she outgoing and good at verbal and eye-contact flirting?), her personality in a broad sense, and other factors like her figure (yours is quite attractive), her hair (ditto), and her style of dress, which can send a strong sexual message (or not).
Thus, I suggest approaching this in an experimental way. If you want to attract and fuck men other than your husband , go ahead and begin doing so. (If this is your goal, incidentally, I encourage you to forge ahead — you have the appearance of a woman who could be sexually very successful, if you aren't already — meaning, if you've been faithful to your husband up 'til now.)
Then, after some period of time you judge sufficient to make a judgment, decide whether you're experiencing "reasonably good" success attracting and seducing men. If so, define your breasts as exactly the right size. If not, re-visit the question of whether to enlarge them to C or D size... and if you have the financial resources and decide you want to do so, go ahead.
You should also, of course, carefully look into the possible or likely medical disadvantages of artificial breast enhancement over the long term; say, 10+ years. I can't comment on this, but I think there's a lot of information on this "out there" in cyberspace and elsewhere. It certainly would not be unreasonable to talk with a woman physician about possible long-term complications.
Good luck with your sexual quests, and may you successfully keep your cuckold in line!
Best regards—
Custer