Since DXF group 70 is bit coded, you should use a bitwise filter for the test, e.g.:
(setq ssvalid (ssget "_X" (list (cons 8 validlistlayers) (cons 0 validlisttype) '(-4 . "&=") '(70 . 1))))
The use of the bitwise filter &= is equivalent to:
(= 1 (logand 1 (cdr (assoc 70 <dxf data>))))
You can find more information about the bitwise masked equals operator in my ssget reference here.
The reason that your original code is failing is because you have included two values for DXF group 70 in your filter list, and all items in the filter list have an implied AND logic - as such, this filter will never select any objects, as DXF group 70 cannot be both 1 and 129.