You have an SLR, and that can teach you an awful lot about what is possible with a half decent camera... it just needs film, which can make it expensive.
However, I DONT actually agree that modern digital has yet achieved the same image quality that film 'may' deliver.... but it has achieved an image quality that's more than acceptable for most uses, and tends to be cheaper and or more convenient for most people.
At £1 a roll for film, and perhaps a fiver to get it developed, you can buy maybe 50 films, maybe 1800 pictures, before you have spent as much as a digital SLR, and you don't have to find all the cash upfront.
Its a good start.
The restrictions imposed by film; the conciouse reminder every time you load one, its costing money; impediment that the whole roll is a single ISO rating you cant change between frames, its all the sort of stuff that makes you think a bit more about what you are about, and use your frames more pudently, rather than firing away, letting the camera do all the work, then trying to make sense of it after.
Its as likely to be better learning therfore.
BUT... its about investing in a system.
Soon as you start thinking you want to try a different lens, or buy a flash-gun, you are going to be in a dilemah, that anything you spend on stuff to support the pentax... is possibly going to be rendered redundant in the near future, if you expect to go digital.... though there is a lot to be said for teh fact that a lot of stuff for obsolete film systems is cheap, and you can get a lot more and better bits of kit for your cash.
Problem I had.... I was given an Olympus OM10 in 1989... meant that through the 1990's I got more and more entrenched with more and more OM system 'stuff', so to switch horses and say go Nikon, meant I had an awful lot of stuff, that was an awful lot more expensive to replace to get the same level of capability as I was carrying around in the Olympus bag!
BUT... buy into the 'wrong' digital system, or buy the wrong bits of kit in the right system in Digital, you may not be any better off....
I have just bought my Nikon D3200. Its a crop sensor camera, and I only have the kit 18-55 lens for it...
Technically I can mount any of the legacy Nikon lenses made in the last half century; but all the old Manual Focus lenses are a pain in the bum, becouse the camera wont give any meter-info through them, let alone any auto-exposure modes. Means using a seperate hand-held meter if I wanted to use them.
Also, Nikon switched technology, and early AF lenses were driven by a motor in the camera, which my camera doesn;t have.... so these lenses, which are often cheaper
second hand, are of limited use. some may allow meter modes on my camera, but they wont focus.
Finally, its a cop-sensor camera, and the kit lens is optimised for a crop sensor... put it on a full-frame sensor camera and its likely it wont give full coverage over the sensor and I'd likely suffer some masking or at least vignetting at the frame edges.
So, IF I buy another lens, say a 55-300... do I buy the cheaper crop sensor DX lens that will work great with this camera, or do I find the extra money to buy the full-frame 70-300 that would do the same job, but would be garanteed to work on a full-frame camera if I upgrade later?
I have little intension of going full-frame, so I am likely to get DX lenses if / when I get any more... but even so.... it's something worth considering.
And at the moment, if I want to do anything more adventurouse... I am back to buying film, so I can use one of my long lenses or the fish-eye or whatever.
So, before you leap in... its very well worth while, pondering where you think you may go, and taking a heads up and considering long term options.
Buying
second hand, just to get in the game, could steer you down an avenue that's less helpful, or make it more expensive to get where you want to go.
So for now... I reccomend getting to know your Pentax. Spending some money on film, getting some pictures with it, and saving up a bit.
When you have some better ideas of what you are doing, what you want to do, and what would be more useful... and with a little more cash to one side to do it.... then ponder the options again.
Ultimately its a good photographer that takes good pictures, not a good camera.... work on your know how, you'll get better pictures with almost anything.