Smugglers is really way better than it looks, particularly in kingdoms with a fairly obvious path to an engine that you both want the same cards for. Most times when I ignore it, my opponent beats me with it.
The old isotropic stats give smugglers a "win rate with" of 91% and a "win rate without" of 111%. That puts it in the same bracket as herbalist, cache, talisman, saboteur, treasure map, and other cards that you need a good reason to buy. I'm afraid it could be possible that you're a bad judge of smuggler kingdoms.
That's pretty likely (that I'm a bad judge); I've also had several games with Smugglers recently in kingdoms nearly purpose built for it. One of those cards that I kept ignoring, and kept losing because of that decision.
But what I was trying to say earlier is that a player who is more likely to lose is more likely to benefit from Smugglers. If I'm playing someone obviously better than me, and the kingdom otherwise favors Smugglers (lots of good cantrips, key Action cards, etc), I'm more likely to buy it than normal precisely because I can assume my opponent will play nearly optimally and the chance of getting an edge by being a few gains ahead improves my odds of winning, even if by a little bit. A good player playing a bad player has far less incentive to buy Smugglers. In the long run, better players will win more than worse players, so maybe that is a part of why the stats are so skewed on it.
