Cam, head, intake, exhaust and compression ratios are a package. Everything has to work together or the engine will fall on it's face at one place or another. Too much overlap will indeed result in poorer idle quality. With a too big a cam the engine can "lope" a bit at idle. This is because the large overlap lets out too much fresh charge and while the engine doesn't miss, the amount of power produced isn't consistent so at idle it can be "lumpy". How aggressive you go with cams is dependent on how much other work you want to do. More cam timing moves the power band to higher rpm's. More aggressive cam timing means that you're going to spin the engine to higher speeds to make that power. The rest of the system needs to be able to work at those speeds. For instance the heads of M30's are limiting and without head work it doesn't make much sense to run a lot more rpm's. If you put a mild cam in a stock head you can gain some power up to around 6200 rpm, but putting in a 300 - 305 degree cam in a stock M30 head doesn't make much sense since those cams really need to turn around 7000 rpm and give up power in the lower ranges. Remember that your power range is moving up. A mild cam will give up some low end torque, but will help the motor pull stronger to 6200 rpm. A bigger cam won't come in until 3500 but will pull to 7000. Headers help some but you're going to hit a wall without head work. More compression is always more power and I'm a compression guy, but higher octane fuel is a lot more expensive now than it used to be. CR's above 11 are probably not a good idea, something in the 10 to 11 range is fine. More compression helps smooth out the idle so as long as you're willing to put in high test gas more is better. If you don't do any head work a cam like the Ireland 282 will give a nice power boost but to really make the 292 work you would be better off getting a B35 head as that is the best breathing M30 stock head. If you're going to put in a cam you need better valve springs and new rockers. By the time you do that B35 heads are cheap so you can refurbish the whole head, do a 5 angle valve job and leave your stock head in box for the next owner.
To take advantage of an even bigger cam you need more compression, headers, and some head work. With some head work to improve the flow capability and by turning the motor to higher rpm is where the power is. Going to better valve springs will let you spin it to 7000 rpm and with better rockers and springs you can go to 7500. A strong setup for the street would be hotter street cam (around 300 degrees of duration) compression ratio around 11:1. with a ported head and headers.
As for induction if you have FI then they all flow well enough but obviously will require some retuning. If it's an early car sidedrafts are a huge improvement over downdraft carbs and they make a lot sweeter sound. For a 3 liter 40mm Webers work fine and for a 3.5 with head work 45's will work. To make 45's work on a 3.0 you need a big cam, head work, and headers as well as a CR around 11:1. That's a pretty sporty engine but it would be a ton of fun in a lightweight.
It all depends on how far you want to go and how much you want to spend.
