Wouldn’t voters have the injury of possibly having the Republican nominee being ineligible? Thus, all those voters are being denied our right to vote.
I like both Cruz and Trump and, IMO, Cruz is eligible. But I’d like to get a ruling on it sooner than later. Otherwise I can see a scenario where Cruz gets the nomination, the Democrats sue over his eligibility, Cruz is found ineligible, and we end up with Bush as the nominee.
No, they wouldn't. You are not being denied your right to vote, and you are not being denied your right to vote for the candidate of your choice. And the injury you propose is not specific to you nor different from the generalized injury that might apply to the population in general.
It is an open question WHO might have standing or at what point. Most opinions I have seen is that it would have to be another candidate, and that it probably would have to be after they lost. Otherwise the injury is only speculative, so even if they have standing, the court might not consider the issue to be "ripe". Even if the injury might be real for them, if they don't lose, they don't actually suffer the injury.
Most people don't understand how hard it can actually be to get a case in front of a federal court, especially if the case is political in nature.