Let's parse these issues -- because I think you touch upon several valid questions.
1. There is obviously no way to replace a loved one or a hero to our society -- BUT, we can set a standard for redirecting the remaining years of the guilty party -- toward some redeeming effort such as repaying society and/or the survivors. It's not a perfect solution, but it does represent a net positive.
2. Prisons are not resorts. You wouldn't want to live in one, would you? And they vary wildly, so I think the generalizations are kind of a red herring here. A better argument could be made for defining specifically what the death row inmate's existence should be like. Which I've defined as consisting of value-deriving, physical work. I am not an advocate of being soft on prisoners, nor am I one for "cruel or unusual punishment" -- but I would argue that there's a LOT of room between the two extremes. We just need to find the right one to make this work.
3. Fear of the death penalty is a broad misconception. It may or may not deter you and me, but there are MANY factors that will override that deterrent -- poverty, mental illness, addiction, heated conflict, etc. I believe the murder statistics in DP vs non-DP states would more than bear that out.
4. I think we can argue the merits of what defines "slam dunk" for ages and possibly never agree. Being a life or death question, I find that to be the most troubling factor in the whole DP debate, and ultimately the primary reason why I have always been against it. It is simply not acceptable for even ONE innocent person to be murdered by official decree -- that is not and should not ever be what we're about. Which is why I keep going back to the question of what we hope for the punishment to accomplish. Should it be about separating the danger from society (yes), punishing the guilty (yes), deterring the tempted (yes, if possible), revenge/retribution (I would argue NO).
Objectively speaking, I think everything and more can be accomplished without putting anyone to death. Lower costs (vs years of due process (which is non-negotiable)), plus potential revenue recovery via labor, plus a plausible enough deterrent based on a long and unpleasant existence -- that's the way I see it. And then there's the question of what our penal system says about our society and where it's heading. I firmly believe that every incarceration is a result of a societal failure of some kind, where the individual may have done the deed, but with some intervening breakdown providing either the impetus or the facilitation. We need to always ask "why?" and own our failures if we are to actually make progress as a society.