It's normal for lower leaves to become yellow and die as the plant grows. This is because the light doesn't penetrate very deeply to keep those leaves producing. For practicality, you only have to worry about the top half of the plant. If it is green and growing, then your plant is probably alright. Lack of light strength can also account for your plants' lack of bushiness. Your plants are just not getting enough light to support alot of vegetative growth. What energy it has is put towards growing taller and finishing its life cycle. Side branching and lower foliage is neglected in favour of new growth skyward.

Now, about your spotty leaves. Its hard to diagnose a problem over the internet even with pics, but I can give you a few things to check. You say your leaves are not as dark as other peoples'. Alot of the color is strain related but it could mean that they are not getting enough N. This indicates to me that they are nutrient deficient which could be caused by PH lockout. Lockout of nutes could also account for your brown spots. Alot of times this is rightly diagnosed as Nutrient deficiency but is treated by adding more nutrients, when in fact it doesn't matter if you add more nutes they are locked out and can't be used by the plant anyways. The remedy is to adjust your PH to within the normal range, whatever your method of growing. You say rockwool so I assume you are doing hydro so the PH for that is 5.5-5.8, I believe. Better to double check that as I do soil only and soil can be a bit higher.

Since you don't give many details about your setup, I can only speculate but that should give you some idea of where to start looking for an answer. If your PH, temp, nutrients levels are all good, then I would look for pests. Hope this helps.

By the way, those plants look pretty healthy to me, you are not doing too badly. I would increase your light to at least a 250W or even 400 if you can handle it. Your plants will love it.