I have an NRS Endurance splash jacket I use some times, granted the neck and wrists seals are not meant to be water proof but you can make them fairly tight. Chances are when it is cold you are wearing some type of glove with an additional wrist strap. Once this over the wrist of the splash jacket is does a reasonable job of keeping water out. Sure some water seeps in you go swimming.
The reality of mellow stream and lake paddling is usually isn't that deep or that far to a shore. If you happen to fall out of your kayak your PDF keeps your head and neck mostly out of water so you don't get a lot of water in that way and then what you do get is some what constraint by the straps and pressure of your PDF. If you can stand up in the water you just fell in, you really don't have to deal with long immersion scenarios.
On a mellow lake the risk of going into the water is mostly getting in or out of the kayak. If this is the paddling you are doing low-risk and close to shore plus with the usual precautions -- change of clothing, friends, flask of bourbon, then why spend the big bucks on a dry suit outerwear, which need maintenance, when you can get something almost as effective for $150-300.
Sure the dry suit is the ideal and opens up a lot more kayaking options but the cheaper options if used in the right situations have their place.