Lugar probably would have won in Indiana in 2012. Another candidate might have won in Missouri that year. Castle could have won in Delaware in 2012.
At the presidential level, Reagan won as a solid conservative. The other winners, Eisenhower, Nixon, the Bushes, had spottier records. Goldwater, another solid conservative, lost by a landslide.
Put history in perspective. Since Gerald Ford, all moderate Republican nominees have lost Presidential elections.
Yes, Reagan was a solid Conservative and while one could make an argument of the Conservative credentials of Bush 43, for the most part he was far more Conservative than his dad.
As for Castle and Lugar, while I concede they likely would have won their respective elections, what if they would have won? Would they have supported a Conservative agenda or would they have acted more like the Maine twins?
If the Republican Party continues to sell out traditional Conservative values, acting like the Democrat lite party, what have we or the Country actually gained?
I submit that those who turn out to vote in such elections would rather vote for the real thing instead of an imitation, while Conservative voters will mostly just stay home (which looks to be what transpired in the 2012 Presidential Election).