Colin has given a pretty accurate view point on the pros and cons. However as with everything there are always variations and just to stir the 'pot' a bit I offer the following observations.
A motorhome does not necessarily mean having a 2nd car. Many people buy motorhomes that are not much longer than large saloons and fit under the 6 meter price barrier for ferries. These still can provide good space and a washroom. In this case many people who have retired just use it as a daily vehicle as it can be parked in supermarkets without too much fuss. If you havea drive at your home, then no problem. Of course multi story carparks are out of the question. If you wish to leave the vehicle on a sitee, then many people use a scooter, fully automatic and electric start for getting around. saves on finding a parking space as well. Also if you live in a city as I do, then having a car is not that much of an advantage. We use the excellent bus service and again save parking fees, especially as being over 60 I have a free travel bus pass.
They are indeed expensive to buy new but if you were to add the total cost of a new caravan and car then the difference is not so great. Plus the 2nd hand market can throw up anything from a bargain to a 'dog'.
Although there is the possibility of some 'moron' taking your pitch, it does not happen that often to really worry about it, especially on CC/C&CC sites where you can mark your pitch with anice little sign. In Europe you often find tables and chairs 'sitting' on a pitch and you know why.
Motorhomes hold their value better than cars and caravans so if you buy one, you should see a reasonable return after even a fair number of years. Just look at the small ads to see the prices being asked for 10 year old models. Also as it is based on a commercial vehicle it is built stronger and should last longer. The main bug bear is people not using them enough and the engines fail due to lack of use.
The other advantage is the payload. In most motorhomes this is in the order of 500+ kg, show me any caravan that is looking at that. No problems in carrying all that 'junk' you like, and plenty of room for wine on the way back from France.
The main disadvanatage is lack of moving space. Many have to cram quite a lot into a smallish space and if you include a fixedbed, then the living space is restricted. Many often encourage you to use the cab seats, which some like, others not.
Insuring a motorhome is the same as any large car and the tax regime is the same as they are classified as 'private light goods' vehicles.
If you go to France you can use the network of Aires and pay as little as _3 per night.
With all these positives, why do i have a caravan? Well, we did have a motorhome but sold it many years back due to relocating abroad. When we came back we looked at a caravan as we already had a car and we live iin a flat wher we cannot park either a motorhome or caravan. However, the flame is still burning in my mind and we may revert if i can persuade SWMBO to let me part with the cash.
As mentioned above go to one of the big Shows and browse.