The biggest problem a lot of folk have with decorating is they want it finished yesterday. That never works, ask oneself how often you will decorate the room in question, ( not that often) and once its done you have to look at it for a very long time, not to mention the money spent, that can add up to a tidy sum. Its well worth putting in the time and effort to end up with a good job. If you don't think your up to the labour involved, ( and it can be very challenging ) give the job to a professional, albeit a little more expensive, but as I say you will be looking at it for a long time, especially if its in your living room. Paint and paper is not cheap, so why waste money, time and effort. Papering is a skill, so preparation is just as important either way. If you wanted just painted plaster, and you have paper on already, it is almost impossible to regain perfect walls without skimming, the hard way and labour intensive, is elbow grease, and depending on room size can take a few days. Needless to say every bit of paper/ backing of that paper needs to be removed, nine times out of ten, under that old paper will be peeling emulsion paint from years gone by, this is were the main problem comes about, you can spend many hours trying to sand this off, patches here and patches there , sometimes you can get away with feathering some of the bigger areas of the edge of the paint down, but even then you will never get perfection, some of these areas will show there ugly head when you re-paint. (Papering) a thicker paper will reduce a lot of the labour as regards to the remaining emulsion, but as I said papering is a skill , if your looking for a plainish looking wall just to paint, then the right paper is needed (plain) but more importantly the joins need to be butted up perfectly, there is nothing worse than seeing vertical joins, and if you end up with such you've lost what you set out to achieve, you need a thick-ish paper to stand any chance of good joints, if you've not done much papering, to thick a paper and you lose your plain look. Papering is like a lot of jobs, the more you do it the better the results. If your not that good at papering then again it a better investment to pay someone, knowing that the materials you've bought won't get wasted. My opinion would be to plumb for skimming, no paper to buy, no labour apart from ripping old paper off, skimming is not to expensive and you are getting the finnish you want.