to be honest i think your shots are already somewhat near their maximum potential, i do not like cropping pictures, so i guess there will not be anything much to add on to the shots.
on a side note, go to eikin's
site, click on punggol and look at mathilda house section, his is the best series i have ever seen so far. in fact, just look at all his photos on punggol, really godlike. among other things, anyways.
but some advice:
1) always correct the horizon, it is KEY, unless you have very intentional tilt. if you tilt, tilt all the way if you want to tilt. don't tilt a bit, it looks like you salah then too lazy to correct
2) look at good photos, as zoosshh has said. go to the library, pick up lee frost or joe cornish' books, these are probably two very prominent coastal scape shooters.. but please, please, do not just replicate their ideas in singapore setting.. in some sense i am quite sick and tired of seeing 80,000 joe cornishes and lee frosts on pbase/flickr.. develop your own style and way of looking at things, the main lesson to be learnt is how to arrange elements in the photo - what constitutes a good composition, and what is not so strong.
3) you seem to be trying some very interesting ideas, like in 6.. but unfortunately they do not work, do not be discouraged and keep trying new stuff, but first and foremost, get the composition down pat. that is most important, then the technique, like filters, hdr will all come in
4) one way of starting out and making a strong composition is to keep it simple and sweet. find something to focus on, move around such that you eliminate every other prominent thing. for example, if you wish to take a photo of mathilda house, do you think something with the silly lrt station in the back would be easier to compose, or something without the lrt station in the frame would be easier to compose?