There are a number stars that dim in inexplicable ways, and some scientists are assuming that there are partial alien dyson spheres surrounding those stars, and this is why it dims in magnitudes not explainable with planets. 
There are no stars that dim in "inexplicable" ways - we can explicate several mechanisms by which this happens. As far as I'm aware, there are no inexplicably dimming stars.
But the search for exoplanets uses TWO completely different mechanisms.
1) When the spectrum of a star shifts very slightly in frequency in a very regular cyclic pattern over a long period of time (months, years) then this must be due to the "doppler effect" which means that the star is moving very slightly either towards or away from us then back again. We can tell that the star is moving in a small circular motion. This is explained by some other object in the vicinity that's orbiting the star at a period given by the wobble of the star. By measuring the period of the star's wobble, we know the "year length" for this other body - and by measuring the amount of the wobble, we can know the force of gravity between star and other body. Taken together, we can know the mass of this second body. Knowing that mass, we can tell whether this invisible companion is another (dim) star, or a planet or something bizarre like a black hole, or a neutron star. In general the star's wobble may be more complicated than just a simple circular motion - we can use the mathematics of Fourier to decompose that motion into the sum of sinewaves - and each component of the motion indicates a separate orbiting body. Hence we can calculate the number, distances, orbital periods and masses of every planet orbiting the star. Notice that we're NOT using the "dimming" of the star in this case.
2) Sometimes - maybe 5% of the time - the plane in which the planets of some distant star are orbiting happens fortuitiously to bring it's planets between the star and us. So the planets are partially eclipsing the parent star. In this case, we do indeed see a very slight dimming in the star's brightness that happens once every time the planet orbits the star. When we look carefully at the AMOUNT of dimming, we can see that as the planet GRADUALLY occludes the star, the dimming gets greater in a pattern that precisely matches two overlapping circles - this is unlike the dimming patterns of things like rotating stars or stars that are varying in brightness as they run out of Hydrogen fuel or stars that are being occluded by clouds of dust and gas. The rate of change of brightness is EXACTLY characteristic of one small circle overlapping a much larger one. This can really only be a planet orbiting the star. Furthermore, in some cases, we can actually see small changes to the spectrum of the star that are explained by the atmosphere of the planet. Our spectroscopy instruments are not yet sensitive enough to do analysis of the planet's atmospheres - but that is something that'll definitely be examined in the near future. But at the very least, this approach let's us know the diameter of each planet - and the speed at which it's travelling relative to the star.
So - combining these two techniques - we can know the diameter AND the mass of those 5% of exo-planets that eclipse their star. This allows use to calculate their densities - so we can tell whether they are rocky planets or gaseous in nature.
There is yet more richness in the datasets.
When we can analyse the gasses in the atmospheres of these planets - we can look for tell-tale gasses that indicate life - perhaps even things that could only be industrial byproducts that would indicate alien civilizations. Expect to see these kinds of results coming along in the next decade.
But your naive idea that "the star dims a bit" is to completely misunderstand the subtlety and beauty of the studies that are being done here.
If it were ONLY random dimming - we wouldn't see those perfect cyclical patterns in the doppler shift that match the dimming as the planet eclipses the primary. We wouldn't see the circle-on-circle profile of the brightness-versus-time curve that perfectly demonstrate a circular planet orbiting a circular star.
The techniques we use to do this are the exact same techniques that were used to predict the moons of planets in our own solar system - and now that we've sent spacecraft out there to take pictures of them - we have concrete verification (if that were needed) that these techniques really do work.
But of course, in Flat-land, these are just little glowing balls up in the sky doing random and inexplicable things.
Yours is a very sad world. You know nothing, you understand nothing, you can explain nothing - and what few pathetic ideas you do have fall apart like wet tissue paper under even the most superficial examination.
For those who open their eyes - see the elegant physics we have to describe our universe - we can discover and understand so much that is beautiful and amazing.