Update for revised question (original is below)
R' Chaim Shmulevitz in the Derech L'Chaim commentary to Derech Hashem addresses this question. He asks, the Rambam writes that all the Nevi'im wanted Moshiach so that they could settle down and focus on learning Torah, but לפום צערא אגרא (the reward is commensurate to the struggle/effort), so why would they want such?
His answer (paraphrased and embellished) is that our actions create the situation that we are in. If you are born into a Torah observant family, then you may not get much reward for putting on Tefillin just as you were raised to do. But if you grew up without that lifestyle, and you begin putting on Tefillin, years later when it is no longer a struggle for you, you still get reward for creating the situation in which you put on Tefillin regularly. This is the idea of mitzvah goreres mitzvah... schar mitzva mitzva (Pirkei Avos 4:2) - that the reward for the mitzvah is the Heavenly assistance to keep more mitzvos, and since you have brought about that Heavenly assistance, it is included in "calculating" your reward.
So with bringing Moshiach, the Nevi'im wanted Moshiach so that they would be able to learn Torah more easily, and it wouldn't have detracted one iota from the reward associated, because the easiness itself would be part of the reward, as a result of their own mitzvos.
Additionally, R' Yaakov Weinberg explained that wanting Moshiach is a reflection of your realization that the world is incomplete without having the full revelation of Hashem's presence. From this perspective, we don't want Moshiach for our own sake - we want it out of a realization that the world we live in is incomplete, and we feel a tangible lack in the current state of existence.
One final point - wanting Moshiach, despite how it may impact our "personal interests" of how much reward we will get, is important because it shows that we have a real relationship with Hashem. If we were to not want Moshiach so that we can get a higher score, it shows that we are doing Mitzvos out of self-interest, not out of love of Hashem. Wanting Moshiach shows that we are doing Mitzvos not as employees but out of a meaningful, selfless, relationship.
If you do not want Moshiach to come, then you violate the 12th principle of the Rambam. No exceptions are made for why one would or wouldn't want Moshiach to come.
The Rambam describes the implications of not accepting any of the principles as follows (postscript to 13 Principles, introduction to Perek Chelek - I don't know which translation this is (I found it online) but Kapach and Shilat have similar sentiments in their translations):
וּכְשֶׁנִּתְקַלְקֵל לאדם יסוד מאלה היסודות – הרי יָצָא מן הכלל וכפר בעיקר. ונקרא "מִין" וְ"אֶפִּיקוֹרוֹס" וְ"קוֹצֵץ בַּנְּטִיעוֹת". וּמִצְוָה לְשׂוֹנְאוֹ וּלְאַבְּדוֹ.
When someone messes up one of these principles, he has departed from the category [of Israelite] and has fundamentally rejected. He is called a heretic, apikorus, and "cuts down saplings", and it is a mitzvah to hate him and destroy him.
So if you don't want Moshiach, you fall into that category.