Imagine all the churches, cathedrals, minarets, monasteries, temples and other places of worship for tourists to visit. 
More freedom of choice. You wouldn’t have to stick to the religion you were born in, and to the god imposed by that religion. If you had a love problem you could pray to Venus, if you were in a financial difficulty you could implore Mercury, and so on. I’m sure they would help.
Interesting idea, but centralization was also an important reason for polytheistic systems in the ancient world.
Polytheistic systems such as the Greek or Egypytian pantheons tended to come about when individual city states (who each had their own god or diad or trinity) joined together to form larger nations. A pantheon including each city’s god aided political stability.
The Romans did the same thing on an even bigger scale, bringing together gods from all over the ancient world creating a super pantheon that again helped political stability.
The Roman world went even further and syncretised their own religions, Mithraism was a syncretisation of Graeco-Roman and Persian religion, the mysteries of Isis/Serapis a syncretisation of Graeco-Roman and Egyptian religion and Christianity a syncretisation of Graeco-Roman and Jewish religion.
In general we’re still brought up with the idea that monotheistic religion is somehow more advanced than polytheistic religion, which just isn’t the case.
Historically polytheistic religions have tended to be tolerant and willing to accept new gods into the fold, whereas monotheistic religions have tended to produce intolerance and fundamentalism with believers unwilling to accept any god other than their own
Isn’t this tautological? Aren’t you just saying, “Historically, believers in a single God have insisted that there is only one God?”
That’s exactly right, and goes to the heart of the OP’s answer. Kant — and other philosophers since — have explained this line of reasoning quite thoroughly. If you define God (as most theistic philosophers have since Ockham) as supreme being, then the easiest way to illustrate the point is with a reductio, like this:
Suppose it were possible for a being to be supreme but not necessary. Since by definition a necessary being exists in every possible circumstance, then there would always be a necessary being, including in this circumstance. But because a necessary being is also a supreme being, it means that we have two supreme beings — which is impossible owing to the definition of supreme (a superlative). The reductio implies a contradiction and so is not true. It is NOT possible for a being to be supreme but not necessary. Therefore, there is only one supreme being Who is also a necessary being.
See this philosophy lecture (Phil 356) by Robert Koons of the University of Texas, which criticizes the ontological argument, but explains this point.
What’s forcing people to stick with the religion into which they were born assuming they no longer believe in it and want to change?
How do you know that there is such a thing as a “necessary being”. Maybe no being is necessary.
Your argument does not work if no being is necessary.
Can you prove the existence of a necessary being?
If you believe in many gods, your religion is “There are many gods: Venus, Mercury, …”
So, if you start praying to Mercury, you are not switching religions, you are still within the same religion.
And in general, even if you are a monotheist you can switch religions, so there is no advantage to polytheism there.
Finally, even in your example, there is no benefit to polytheism. Monotheism works just as well: “If you had a love problem you could pray to God, if you were in a financial difficulty you could implore God, and so on. I’m sure he would help.”
St. Anselm came up with this well before Kant or even Ockham.
You’re right, Poly. Thanks!
Christianity is not monotheism.
Devils, ghosts, angels, perhaps saints, etc.
All with separate agendas.
Those beings are not supreme and are not worshipped.
Maybe it would be comforting to have a separate god for fighting crabgrass or successful souffles, if you didn’t need a referral from your general practitioner god.
On the other hand, it’s nice to know, when you pray to an omniscient, omnipotent god, that your god knows how to cook omni grits. That’s important.