Water stains mar the ceiling. The floor feels spongy and the whole house has a musty, moldy smell that the best candles can not cover up. Is this the sign of poor housekeeping? While that is certainly possible, it is more likely caused by water damage and from the sounds of things it is a chronic, rather than a recent thing. Your first step is to assess this water damage and then discover the most likely source of it. You will of course need to make necessary repairs to prevent further water damage, and you should consider doing this before you even begin taking care of what is already messed up. There is no sense in putting good money into a cosmetic fix of the water stained ceiling if you do not find and repair its cause.
If the water damage is concentrated in the corners of the ceiling and along the baseboards of the walls, it is likely a loose shingle or faulty eave spout that is allowing water to seep under. The accumulated water will then collect under the ceiling tiles and will result in the tell tale brownish spots of obvious water damage. Of course, the easiest and most foolhardy approaches is simply repainting that portion of the ceiling every few months, but that will do nothing to prevent future water damage, nor will it do anything to repair what already exists.
Hiring a trustworthy handyman to do some needed repairs will be less expensive in the long run than taking a wait and see kind of stance- a collapsed roof can be very costly indeed and because it will never happen at a convenient time, ( and when would be?) you will end up paying top dollar to a roofer. Not only does an improperly maintained roof put you at a high risk for a costly, emergency repair and more devastating water damages, it may negate your homeowner's insurance policy. Do not ever make the mistake of thinking that a seasoned appraiser cannot spot prior, uncared for water damage- they can spot those problems a million miles away.
Water damage that is not centered along the edges of walls may indicate a more serious roofing issue, or in the case of a two story home, a plumbing issue in the upstairs. Again, make sure that you track down and repair the cause of any water damage before you try to restore, revive or replace your items. There is no sense in buying a new duvet for a bed that will just get dripped on in a month or so.
Cosmetic water damage issues aside, there are other more serious health related problems to consider. If the water is leaking down your wall, it might be allowing dangerous black mold to grow rampant- a potential health hazard for the very young, the very old or those with certain lung or immune system disorders. It is in your best interest to track down the cause of your water damage as soon as you find it, and then to repair it. And afterwards you will have the most wonderful excuse for renovation!