The lakes "full" level is only 681' where the FEMA 100 year flood plain for the Lake Travis area is 722'MSL, and the property is at around 705' +/-. the circumstances would be a little different than coast front as it is not mucky soil as suggested.

And so what of the log of repairs, if a stove hasn't been repaired in 20 years, is it more or less likely to go wrong?

I am not saying this is the case because I am in no position to actually know but starting out with a can of worms in one of the surest ways to start out on the wrong foot in real estate investing and one of the worse things you can let happen to you at any time. 

Unless I am calculating this wrong: $1,600*.5 = $800 effective gross revenue. 800 - 280-100=$420. 

Too many young people who want to get rich fast pick the wrong way of doing it.

I agree with @Daniel MohnkernDaniel you being in California has a whole different set of potential problems as my parents have been on the wrong side of this situation and the end result was the tenants got to stay in the property for 9 months and then they had to pay for their moving expenses because of a "perceived" violation of their rights....Anyways as far as whether the property is abandoned if you are getting rent money then I would not disturb it, if you stop getting money and they are gone then thats a different story.

I wouldn't toss a tenant who has done nothing wrong and stayed for 23 years.  

What's wrong with it?

As a person that got into this crazy world as an almost out of work airline pilot with no future potential after 9/11 started buying homes and apartment buildings, after about 20 homes I realized that there were many things I was doing wrong and my business partner and I decided to hand our portfolio over to a PM.

Basically, the more $ in your required rehab &/or the longer the rehab timeline, the bigger your risk, because there are many more opportunities for things to go wrong.