I think that you will find (as I have) that your interest in Lugers will evolve/change as you acquire more...From your basic 'shooter' [mismatched, re-blued, defaced]; to a respectable 'collectible' [read: has flaws but attributable to age/wear] Luger; to a valued 'collectible' [little wear/use]...
There are degrees of each, and permissible defects/upgrades...And a hierarchy of value/desirability, or several, based on individual preferences...(Some mfg's are finely machined, others are rough hewn; etc)...
And there are the wildly exotic variations...
You probably won't know what you really want until you try a couple...and see what other people are collecting...
I've been wading in the shallow end for a couple years now...And now I'm sampling the deep end...cautiously; frugally; and choosing from the pieces that others are offering as they upgrade...
I don't expect to get rich 'collecting' Lugers (or any others), but if I choose carefully, I shouldn't lose my shirt either...
And in the end I'll have a top-grade collectible that I will show off at every opportunity...
(And then I'll die and my niece will sell everything for a couple hundred $$$) 