Sandoval's current hit streak could net you excellent value, and if you can, this might be the time to strike if you think you can get someone to help improve your team. If not, hold onto him. For someone that qualifies at third base, had Sandoval not been injured, a 25+ homer campaign would've been within reach. Perhaps you want to wait until he gains first base qualification to boost his value, or if you bring this up with the manager you're trading with, bringing it in discussions might be good enough.
Like your scenario you proposed.
Keeper League:
F) N.Backstrom, E.Malkin, V.Lecavalier, P.Mueller, A.Mcdonald, B.Boyes, A.Hemsky, S.Horcoff, K.Turris, D.Jeffrey, M.Perreault, C.O'Reilly, S.Upshall, M.Erat, S.Gagne, D.Legwand D) S.Souray, M.Streit, A.Babchuk, T.Gilbert, I.Cole, J.Hillen, M.Methot G) B.Elliott, S.Varlamov, C.Ward, J.Reimer P) N.Kadri, E.Kuznetsov, S.Shirokov, V.Tarasenko, J.Blum, OEL, J.Moore, O.Pavelec