1) It seems to me that magic users get to use considerably less spells per day in RM than in D&D, which is not a huge problem as I like a low magic campaign; given that this may be the case is it wise for spell users to develop plenty of skills elsewhere in order to remain effective in a traditional adventuring group? If so, what would be the value of investing development points into a spell list above the level of spell you can cast?
Couple of things to point out.
First of all, RMX gives magic using characters more power points than the core RMC rules to. This is, in part, to make them more viable overall. Express Additions #3 contains an option called Fast PP Regen, which allows a character to regain their Power Points faster than the core rules allow (i.e. core requires that they sleep for 8 hours), at a rate of about 5 or 10 minutes of complete rest per power point. When using that option, PP is a measure of how much power they can handle before requiring rest, not a measure of how much they have.
Spell users in RMX cannot cast spells above their level, regardless of whether or not they know them (this is the same as the core RMC). However, if a character DOES know a spell above his level, and he gains enough experience to go up a level while adventuring, that spell then becomes immediately available and usable without the character having to go train first. (This also depends on how you handle levelling up - if you don't require PCs to get to a location to train before allowing them to spend xp, then this is moot).
RMC's Spell Law does contain options (ESF) which will allow characters to cast spells above their level (in exchange for a larger fumble range, and much greater chance of damaging themselves should they fumble). In hindsight, I wish that we had included this in RMX, even if in a truncated form (such as the option found in Express Additions #3).
2) Spell Duration; under "duration (C)" it clearly states if the caster stops concentrating the spell temporarily ceases but can be picked up again by the caster if they re-concentrate as long as the duration has not expired, so no problem with that. However, when just "C" is listed there is a lack of clarity. If the caster ceases concentration does the spell end? Or, can it be restarted again as with the above listing? (I'm assuming not at this stage because that would effectively mean the spell has an unlimited duration in effect.) If another spell is cast while concentrating does the current spell end?
Spells with a duration of "C" (without any other duration listed) will immediately end and cannot be resumed once the caster stops concentrating. (and note: being stunned will definitely stop a character from concentrating, for other damage, I would recommend having them make a Self Discipline roll to maintain concentration if damaged - there are no official rules for this, so you can handle it however you like.)
Also, look at the end of the first entry on page 26 - it specifically states that a caster cannot cast another spell while concentrating.
Those spells that have both duration and concentration allow the caster to stop concentrating, cast another spell, and then pick up where he left off with the first spell.
3) Spell descriptions are very basic compared with D&D/Pathfinder; not sure yet whether this is a strength or a weakness. Is this brevity of explanation carried on into Spell Law?
Yes -- I think that the idea was partly to save space (originally, that is - the same descriptions (and description type) have essentially carried over into all versions of RM), and partly to allow the GM to customize them to the setting to some degree (i.e. 2 clerics casting the same spell might have it look very differently).
Use this to your advantage! Have players customize the looks of their spells (within reason) so that their version of a shock bolt is different from another caster's version. Have fun with it.
