Are the words necessary?

I don't know where to start. That is a sentence which is fraught with more melodrama than the subject deserves.

There's nothing wrong with "sincerely." The locution "actual achievement" is rather awkward.

Maybe something like this:

I sincerely hope that our club will achieve an increasing in membership of 50 percent by 2015, the year of the 50th anniversary.

I don't think you need to be praying, unless the club is of a religious nature. You also don't need to repeat club, once is enough.

I hope we can achieve a 50% increase in membership to honor the 50th anniversary of the club.

Regardless of style, grammatically, the answer is no, they are not necessary at all.

fancy a threesome?

Can one pray insincerely?

Sure, but what's its intrinsic value, then?