I agree with the above but for a different reason... At times I am a cheap SOB

so I try to make your current bike work for you before moving onto something else.. I do have a few suggestions,
First is a flywheel weight. I had a KX 250, to which I added a flywheel weight. At 1st I really didn't notice it, but the more I road it the more it shined. It doesn't reduce the "hit" by a lot, but make the bike easier to ride, less prone to stalling, with more tractable power. Second is jetting.. you can "richen" up your jetting just a tad and gain a little more bottom end. Then there's suspension... it makes a world of difference with the boingers set properly. Proper suspension will allow you to gain confidence in the bike and its ability to save your arse when you make a mistake. (Let's face it we all make riding mistakes)
A 150 is a fun bike, it requires some more input to go fast, but it really does reward the rider for its hard work. No matter your weight, either bike will put t huge smile on your face.
One last thought, what are your true expectations when riding / racing... I like many others have a few (20) years on you... I know my days of being a MX star are behind me. I also know that I am a B-, C+ rider in the Cross Country races. At this point I ride for the fun, and the thrill. I have no grand illusions of where my talent (or lack there of) will take me, and ride for fun, not to mention beating the crap out of my body.