I have an issue with blow-by on my vr4. Thing is I don't know where it's coming from. I've secured the dipstick down with a spring. The only other place I can suspect is the oil cap. How likely is that to be the culprit?

I'd start with a compression test. I've just replaced worn out dipsticks and that's always worked for me, so if a spring isn't holding it down, you might have a bigger problem.

A clogged PVC valve might be causing extra pressure? Maybe...

Check PCV.

What's making you think there is so much blowby? The dipstick "seal" hardens up and can blow out on a normal healthy motor. Feel the rubber part at the top, it likely is dry and doesn't feel like rubber. That is what makes them pop out. I personally prefer 2g dipsticks anyways (different style)

Also, the oil cap gasket also has the same issue, and dries out and leaks, even on a healthy motor. A new gasket is like $2.

Guess I need to check all 3.
But the reason I say I have blow-by is because anything over 15lbs and the spark plug valley has a good bit of oil in it. And based by the splatter on the underside of the hood, it's coming from the driver side. Hard to distinguish between the dipstick and the cap though. Might still be the dipstick.

How well is your PCV system working?

Start with cap gasket for sure

In addition to what everyone has said what about the Valve Cover Gasket, more specifically the four circular gaskets for each Spark Plug well?

You mentioned the Spark Plug “Valley” has a bit of oil so I would start with the Valve Cover Gasket.

Felpro kit comes with everything needed. At least what I've been ordering from rock auto.

Half moon piece, valve cover gasket, spark plug gaskets.

Just be sure to clean everything. If you don't remove everything old, it won't seal.

I still use a little gasket maker too. helps hold the gasket in place and it's needed for the half moon piece anyway.

Let cure over night. If you do it right, it will last years. If you rush it, it won't.

I've never had any luck with the stock size PVC system. Everyone upgrades the line size for a reason.

In my case I drill and tap the valve covers with 1/4" npt fittings, drill out the inside of 14mm barb to 1/4"brass fittings and sweat in a piece of copper tube with some holes drills in it. I polish the area under the VC baffle. I then drill and tap the intake manifold for a 1/4nptx14mm fitting. Intake tube gets the same fitting. Its a bit of effort but keeps everything working better, doesn't require welding and I'm not a huge fan of the an fitting look.

The only leak I had to deal with was the cas o ring, but they just fail after a while. Took care of that recently.
This has worked well to improve the overall efficiency of the system.