Impact signal is mixed year-to-year but net .... not an impactful player.
https://sites.google.com/site/rapmstats/97-14-rapm-2 has him as slight negative in the full play-by-play era.
RAPM estimates 94-96 seem to have him near neutral, slight negative each year, with on-off looking slightly better in '95.
(player, net on-off (per 48 min iirc), Regressed RAPM, RAPM adj w/Variance
'94 Spree, -0.9, 0.07, 0.09
'95 Spree, 3.2, -0.63, -0.81
'96 Spree, -2.1, -0.73, -0.81
(fwiw that positive '95 is driven by a great defensive number overcoming a bad offensive number).
Another note, as someone who had some hype as dunker (at least a little, for instance I remember a mag giving odds of him among others winning a dunk contest, before contestants were announced), he didn't dunk much by the end (2 dunks in his final season, though he also had a down year of 7 in 2001 - he'd had 40 in '93, 46 in '97).
Reference box-composites see him as mostly around average, career and for each year (PER most favorable, WS/48 least). '97 an outlier efficiency year, as well as one of his higher volumes is seen by PER and BPM as his clear best year. Fwiw, it's his best on-off at +10.7 but they still weren't great with him on and RAPM whilst clearly positive is a lot closer to average (+1.22 at
https://ascreamingcomesacrossthecourt.blogspot.com/2013/10/introducing-1990s-rapm.html).