Another vote for the extra lighting !
Depending on the plants you choose, you may actually need to change the lighting, filter and substrate to have much success, but I'd cerainly start with the lighting.
I dont agree with the statement that
lighting usually isn't a huge factor in the health of plants ! It's often far more important to plants than the filtration method !
Are you sure it's 11W and 29 Gals. That seems very low, 11w seems more suitable for 29 Litres ! A good rule of thumb for lighting in a planted tank is to aim for 2 watts per gallon (US gallons).
The filter is also important for the overall health of the tank and it's occupants, but there are methods where you can actually have a planted tank without any filtration (
Walstad 'Natural' method) ! However as with all things, you need to have things balanced correctly for that to work.
I'm not sure what you mean by a 'top filter', but the only one that would give you real problems with plants is an Under Gravel Filter. An external filter is certainly your best choice and ideally you should upgrade the lighting AND the filter at the same time ..... but if that's not possible, I'd still say
do the lighting first !